1stunnel(8) stunnel TLS Proxy stunnel(8)
2
6 stunnel - TLS offloading and load-balancing proxy
7
9 Unix:
10 stunnel [FILE] | -fd N | -help | -version | -sockets | -options
11 WIN32:
13 stunnel [ [ -install | -uninstall | -start | -stop |
14 -reload | -reopen | -exit ] [-quiet] [FILE] ] |
15 -help | -version | -sockets | -options
16
18 The stunnel program is designed to work as TLS encryption wrapper
19 between remote clients and local (inetd-startable) or remote servers.
20 The concept is that having non-TLS aware daemons running on your system
21 you can easily set them up to communicate with clients over secure TLS
22 channels.
23 stunnel can be used to add TLS functionality to commonly used Inetd
25 daemons like POP-2, POP-3, and IMAP servers, to standalone daemons like
26 NNTP, SMTP and HTTP, and in tunneling PPP over network sockets without
27 changes to the source code.
28 This product includes cryptographic software written by Eric Young
30 (eay@cryptsoft.com)
31
33 FILE
34 Use specified configuration file
35 -fd N (Unix only)
37 Read the config file from specified file descriptor
38 -help
40 Print stunnel help menu
41 -version
43 Print stunnel version and compile time defaults
44 -sockets
46 Print default socket options
47 -options
49 Print supported TLS options
50 -install (Windows NT and later only)
52 Install NT Service
53 -uninstall (Windows NT and later only)
55 Uninstall NT Service
56 -start (Windows NT and later only)
58 Start NT Service
59 -stop (Windows NT and later only)
61 Stop NT Service
62 -reload (Windows NT and later only)
64 Reload the configuration file of the running NT Service
65 -reopen (Windows NT and later only)
67 Reopen the log file of the running NT Service
68 -exit (Win32 only)
70 Exit an already started stunnel
71 -quiet (Win32 only)
73 Don't display any message boxes
74
76 Each line of the configuration file can be either:
77 · An empty line (ignored).
79 · A comment starting with ';' (ignored).
81 · An 'option_name = option_value' pair.
83 · '[service_name]' indicating a start of a service definition.
85 An address parameter of an option may be either:
87 · A port number.
89 · A colon-separated pair of IP address (either IPv4, IPv6, or domain
91 name) and port number.
92 · A Unix socket path (Unix only).
94 GLOBAL OPTIONS
96 chroot = DIRECTORY (Unix only)
97 directory to chroot stunnel process
98 chroot keeps stunnel in a chrooted jail. CApath, CRLpath, pid and
100 exec are located inside the jail and the patches have to be
101 relative to the directory specified with chroot.
102 Several functions of the operating system also need their files to
104 be located within the chroot jail, e.g.:
105 · Delayed resolver typically needs /etc/nsswitch.conf and
107 /etc/resolv.conf.
108 · Local time in log files needs /etc/timezone.
110 · Some other functions may need devices, e.g. /dev/zero or
112 /dev/null.
113 compression = deflate | zlib
115 select data compression algorithm
116 default: no compression
118 Deflate is the standard compression method as described in RFC
120 1951.
121 debug = [FACILITY.]LEVEL
123 debugging level
124 Level is one of the syslog level names or numbers emerg (0), alert
126 (1), crit (2), err (3), warning (4), notice (5), info (6), or debug
127 (7). All logs for the specified level and all levels numerically
128 less than it will be shown. Use debug = debug or debug = 7 for
129 greatest debugging output. The default is notice (5).
130 The syslog facility 'authpriv' will be used unless a facility name
132 is supplied. (Facilities are not supported on Win32.)
133 Case is ignored for both facilities and levels.
135 EGD = EGD_PATH (Unix only)
137 path to Entropy Gathering Daemon socket
138 Entropy Gathering Daemon socket to use to feed the OpenSSL random
140 number generator.
141 engine = auto | ENGINE_ID
143 select hardware or software cryptographic engine
144 default: software-only cryptography
146 See Examples section for an engine configuration to use the
148 certificate and the corresponding private key from a cryptographic
149 device.
150 engineCtrl = COMMAND[:PARAMETER]
152 control hardware engine
153 engineDefault = TASK_LIST
155 set OpenSSL tasks delegated to the current engine
156 The parameter specifies a comma-separated list of task to be
158 delegated to the current engine.
159 The following tasks may be available, if supported by the engine:
161 ALL, RSA, DSA, ECDH, ECDSA, DH, RAND, CIPHERS, DIGESTS, PKEY,
162 PKEY_CRYPTO, PKEY_ASN1.
163 fips = yes | no
165 enable or disable FIPS 140-2 mode.
166 This option allows you to disable entering FIPS mode if stunnel was
168 compiled with FIPS 140-2 support.
169 default: no (since version 5.00)
171 foreground = yes | quiet | no (Unix only)
173 foreground mode
174 Stay in foreground (don't fork).
176 With the yes parameter it also logs to stderr in addition to the
178 destinations specified with syslog and output.
179 default: background in daemon mode
181 iconActive = ICON_FILE (GUI only)
183 GUI icon to be displayed when there are established connections
184 On Windows platform the parameter should be an .ico file containing
186 a 16x16 pixel image.
187 iconError = ICON_FILE (GUI only)
189 GUI icon to be displayed when no valid configuration is loaded
190 On Windows platform the parameter should be an .ico file containing
192 a 16x16 pixel image.
193 iconIdle = ICON_FILE (GUI only)
195 GUI icon to be displayed when there are no established connections
196 On Windows platform the parameter should be an .ico file containing
198 a 16x16 pixel image.
199 log = append | overwrite
201 log file handling
202 This option allows you to choose whether the log file (specified
204 with the output option) is appended or overwritten when opened or
205 re-opened.
206 default: append
208 output = FILE
210 append log messages to a file
211 /dev/stdout device can be used to send log messages to the standard
213 output (for example to log them with daemontools splogger).
214 pid = FILE (Unix only)
216 pid file location
217 If the argument is empty, then no pid file will be created.
219 pid path is relative to the chroot directory if specified.
221 RNDbytes = BYTES
223 bytes to read from random seed files
224 RNDfile = FILE
226 path to file with random seed data
227 The OpenSSL library will use data from this file first to seed the
229 random number generator.
230 RNDoverwrite = yes | no
232 overwrite the random seed files with new random data
233 default: yes
235 service = SERVICE (Unix only)
237 stunnel service name
238 The specified service name is used for syslog and as the inetd mode
240 service name for TCP Wrappers. While this option can technically
241 be specified in the service sections, it is only useful in global
242 options.
243 default: stunnel
245 syslog = yes | no (Unix only)
247 enable logging via syslog
248 default: yes
250 taskbar = yes | no (WIN32 only)
252 enable the taskbar icon
253 default: yes
255 SERVICE-LEVEL OPTIONS
257 Each configuration section begins with a service name in square
258 brackets. The service name is used for libwrap (TCP Wrappers) access
259 control and lets you distinguish stunnel services in your log files.
260 Note that if you wish to run stunnel in inetd mode (where it is
262 provided a network socket by a server such as inetd, xinetd, or
263 tcpserver) then you should read the section entitled INETD MODE below.
264 accept = [HOST:]PORT
266 accept connections on specified address
267 If no host specified, defaults to all IPv4 addresses for the local
269 host.
270 To listen on all IPv6 addresses use:
272 accept = :::PORT
274 CApath = DIRECTORY
276 Certificate Authority directory
277 This is the directory in which stunnel will look for certificates
279 when using the verifyChain or verifyPeer options. Note that the
280 certificates in this directory should be named XXXXXXXX.0 where
281 XXXXXXXX is the hash value of the DER encoded subject of the cert.
282 The hash algorithm has been changed in OpenSSL 1.0.0. It is
284 required to c_rehash the directory on upgrade from OpenSSL 0.x.x to
285 OpenSSL 1.x.x.
286 CApath path is relative to the chroot directory if specified.
288 CAfile = CA_FILE
290 Certificate Authority file
291 This file contains multiple CA certificates, to be used with the
293 verifyChain and verifyPeer options.
294 cert = CERT_FILE
296 certificate chain file name
297 The parameter specifies the file containing certificates used by
299 stunnel to authenticate itself against the remote client or server.
300 The file should contain the whole certificate chain starting from
301 the actual server/client certificate, and ending with the self-
302 signed root CA certificate. The file must be either in PEM or P12
303 format.
304 A certificate chain is required in server mode, and optional in
306 client mode.
307 This parameter is also used as the certificate identifier when a
309 hardware engine is enabled.
310 checkEmail = EMAIL
312 email address of the peer certificate subject
313 Multiple checkEmail options are allowed in a single service
315 section. Certificates are accepted if no subject checks were
316 specified, or the email address of the peer certificate matches any
317 of the email addresses specified with checkEmail.
318 This option requires OpenSSL 1.0.2 or later.
320 checkHost = HOST
322 host of the peer certificate subject
323 Multiple checkHost options are allowed in a single service section.
325 Certificates are accepted if no subject checks were specified, or
326 the host name of the peer certificate matches any of the hosts
327 specified with checkHost.
328 This option requires OpenSSL 1.0.2 or later.
330 checkIP = IP
332 IP address of the peer certificate subject
333 Multiple checkIP options are allowed in a single service section.
335 Certificates are accepted if no subject checks were specified, or
336 the IP address of the peer certificate matches any of the IP
337 addresses specified with checkIP.
338 This option requires OpenSSL 1.0.2 or later.
340 ciphers = CIPHER_LIST
342 Select permitted TLS ciphers
343 A colon-delimited list of the ciphers to allow in the TLS
345 connection, for example DES-CBC3-SHA:IDEA-CBC-MD5.
346 client = yes | no
348 client mode (remote service uses TLS)
349 default: no (server mode)
351 config = COMMAND[:PARAMETER]
353 OpenSSL configuration command
354 The OpenSSL configuration command is executed with the specified
356 parameter. This allows any configuration commands to be invoked
357 from the stunnel configuration file. Supported commands are
358 described on the SSL_CONF_cmd(3ssl) manual page.
359 Several config lines can be used to specify multiple configuration
361 commands.
362 This option requires OpenSSL 1.0.2 or later.
364 connect = [HOST:]PORT
366 connect to a remote address
367 If no host is specified, the host defaults to localhost.
369 Multiple connect options are allowed in a single service section.
371 If host resolves to multiple addresses and/or if multiple connect
373 options are specified, then the remote address is chosen using a
374 round-robin algorithm.
375 CRLpath = DIRECTORY
377 Certificate Revocation Lists directory
378 This is the directory in which stunnel will look for CRLs when
380 using the verifyChain and verifyPeer options. Note that the CRLs in
381 this directory should be named XXXXXXXX.r0 where XXXXXXXX is the
382 hash value of the CRL.
383 The hash algorithm has been changed in OpenSSL 1.0.0. It is
385 required to c_rehash the directory on upgrade from OpenSSL 0.x.x to
386 OpenSSL 1.x.x.
387 CRLpath path is relative to the chroot directory if specified.
389 CRLfile = CRL_FILE
391 Certificate Revocation Lists file
392 This file contains multiple CRLs, used with the verifyChain and
394 verifyPeer options.
395 curve = NID
397 specify ECDH curve name
398 To get a list of supported curves use:
400 openssl ecparam -list_curves
402 default: prime256v1
404 logId = TYPE
406 connection identifier type
407 This identifier allows you to distinguish log entries generated for
409 each of the connections.
410 Currently supported types:
412 sequential
414 The numeric sequential identifier is only unique within a
415 single instance of stunnel, but very compact. It is most
416 useful for manual log analysis.
417 unique
419 This alphanumeric identifier is globally unique, but longer
420 than the sequential number. It is most useful for automated
421 log analysis.
422 thread
424 The operating system thread identifier is neither unique (even
425 within a single instance of stunnel) nor short. It is most
426 useful for debugging software or configuration issues.
427 process
429 The operating system process identifier (PID) may be useful in
430 the inetd mode.
431 default: sequential
433 debug = LEVEL
435 debugging level
436 Level is a one of the syslog level names or numbers emerg (0),
438 alert (1), crit (2), err (3), warning (4), notice (5), info (6), or
439 debug (7). All logs for the specified level and all levels
440 numerically less than it will be shown. Use debug = debug or debug
441 = 7 for greatest debugging output. The default is notice (5).
442 delay = yes | no
444 delay DNS lookup for the connect option
445 This option is useful for dynamic DNS, or when DNS is not available
447 during stunnel startup (road warrior VPN, dial-up configurations).
448 Delayed resolver mode is automatically engaged when stunnel fails
450 to resolve on startup any of the connect targets for a service.
451 Delayed resolver inflicts failover = prio.
453 default: no
455 engineId = ENGINE_ID
457 select engine ID for the service
458 engineNum = ENGINE_NUMBER
460 select engine number for the service
461 The engines are numbered starting from 1.
463 exec = EXECUTABLE_PATH
465 execute a local inetd-type program
466 exec path is relative to the chroot directory if specified.
468 The following environmental variables are set on Unix platforms:
470 REMOTE_HOST, REMOTE_PORT, SSL_CLIENT_DN, SSL_CLIENT_I_DN.
471 execArgs = $0 $1 $2 ...
473 arguments for exec including the program name ($0)
474 Quoting is currently not supported. Arguments are separated with
476 an arbitrary amount of whitespace.
477 failover = rr | prio
479 Failover strategy for multiple "connect" targets.
480 rr round robin - fair load distribution
482 prio
484 priority - use the order specified in config file
485 default: prio
487 ident = USERNAME
489 use IDENT (RFC 1413) username checking
490 include = DIRECTORY
492 include all configuration file parts located in DIRECTORY
493 The files are included in the ascending alphabetical order of their
495 names. The recommended filename convention is
496 for global options:
498 00-global.conf
500 for local service-level options:
502 01-service.conf
504 02-service.conf
506 key = KEY_FILE
508 private key for the certificate specified with cert option
509 A private key is needed to authenticate the certificate owner.
511 Since this file should be kept secret it should only be readable by
512 its owner. On Unix systems you can use the following command:
513 chmod 600 keyfile
515 This parameter is also used as the private key identifier when a
517 hardware engine is enabled.
518 default: the value of the cert option
520 libwrap = yes | no
522 Enable or disable the use of /etc/hosts.allow and /etc/hosts.deny.
523 default: no (since version 5.00)
525 local = HOST
527 By default, the IP address of the outgoing interface is used as the
528 source for remote connections. Use this option to bind a static
529 local IP address instead.
530 OCSP = URL
532 select OCSP responder for certificate verification
533 OCSPaia = yes | no
535 validate certificates with their AIA OCSP responders
536 This option enables stunnel to validate certificates with the list
538 of OCSP responder URLs retrieved from their AIA (Authority
539 Information Access) extension.
540 OCSPflag = OCSP_FLAG
542 specify OCSP responder flag
543 Several OCSPflag can be used to specify multiple flags.
545 currently supported flags: NOCERTS, NOINTERN, NOSIGS, NOCHAIN,
547 NOVERIFY, NOEXPLICIT, NOCASIGN, NODELEGATED, NOCHECKS, TRUSTOTHER,
548 RESPID_KEY, NOTIME
549 OCSPnonce = yes | no
551 send and verify the OCSP nonce extension
552 This option protects the OCSP protocol against replay attacks. Due
554 to its computational overhead, the nonce extension is usually only
555 supported on internal (e.g. corporate) responders, and not on
556 public OCSP responders.
557 options = SSL_OPTIONS
559 OpenSSL library options
560 The parameter is the OpenSSL option name as described in the
562 SSL_CTX_set_options(3ssl) manual, but without SSL_OP_ prefix.
563 stunnel -options lists the options found to be allowed in the
564 current combination of stunnel and the OpenSSL library used to
565 build it.
566 Several option lines can be used to specify multiple options. An
568 option name can be prepended with a dash ("-") to disable the
569 option.
570 For example, for compatibility with the erroneous Eudora TLS
572 implementation, the following option can be used:
573 options = DONT_INSERT_EMPTY_FRAGMENTS
575 default:
577 options = NO_SSLv2
579 options = NO_SSLv3
580 protocol = PROTO
582 application protocol to negotiate TLS
583 This option enables initial, protocol-specific negotiation of the
585 TLS encryption. The protocol option should not be used with TLS
586 encryption on a separate port.
587 Currently supported protocols:
589 cifs
591 Proprietary (undocummented) extension of CIFS protocol
592 implemented in Samba. Support for this extension was dropped
593 in Samba 3.0.0.
594 connect
596 Based on RFC 2817 - Upgrading to TLS Within HTTP/1.1, section
597 5.2 - Requesting a Tunnel with CONNECT
598 This protocol is only supported in client mode.
600 imap
602 Based on RFC 2595 - Using TLS with IMAP, POP3 and ACAP
603 nntp
605 Based on RFC 4642 - Using Transport Layer Security (TLS) with
606 Network News Transfer Protocol (NNTP)
607 This protocol is only supported in client mode.
609 pgsql
611 Based on
612 http://www.postgresql.org/docs/8.3/static/protocol-flow.html#AEN73982
613 pop3
615 Based on RFC 2449 - POP3 Extension Mechanism
616 proxy
618 Haproxy client IP address
619 http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt
620 smtp
622 Based on RFC 2487 - SMTP Service Extension for Secure SMTP over
623 TLS
624 socks
626 SOCKS versions 4, 4a, and 5 are supported. The SOCKS protocol
627 itself is encapsulated within TLS encryption layer to protect
628 the final destination address.
629 http://www.openssh.com/txt/socks4.protocol
631 http://www.openssh.com/txt/socks4a.protocol
633 The BIND command of the SOCKS protocol is not supported. The
635 USERID parameter is ignored.
636 See Examples section for sample configuration files for VPN
638 based on SOCKS encryption.
639 protocolAuthentication = AUTHENTICATION
641 authentication type for the protocol negotiations
642 Currently, this option is only supported in the client-side
644 'connect' and 'smtp' protocols.
645 Supported authentication types for the 'connect' protocol are
647 'basic' or 'ntlm'. The default 'connect' authentication type is
648 'basic'.
649 Supported authentication types for the 'smtp' protocol are 'plain'
651 or 'login'. The default 'smtp' authentication type is 'plain'.
652 protocolDomain = DOMAIN
654 domain for the protocol negotiations
655 Currently, this option is only supported in the client-side
657 'connect' protocol.
658 protocolHost = HOST:PORT
660 destination address for the protocol negotiations
661 protocolHost specifies the final TLS server to be connected to by
663 the proxy, and not the proxy server directly connected by stunnel.
664 The proxy server should be specified with the 'connect' option.
665 Currently the protocol destination address only applies to the
667 'connect' protocol.
668 protocolPassword = PASSWORD
670 password for the protocol negotiations
671 Currently, this option is only supported in the client-side
673 'connect' and 'smtp' protocols.
674 protocolUsername = USERNAME
676 username for the protocol negotiations
677 Currently, this option is only supported in the client-side
679 'connect' and 'smtp' protocols.
680 PSKidentity = IDENTITY
682 PSK identity for the PSK client
683 PSKidentity can be used on stunnel clients to select the PSK
685 identity used for authentication. This option is ignored in server
686 sections.
687 default: the first identity specified in the PSKsecrets file.
689 PSKsecrets = FILE
691 file with PSK identities and corresponding keys
692 Each line of the file in the following format:
694 IDENTITY:KEY
696 The key is required to be at least 20 characters long. The file
698 should not be world-readable nor world-writable.
699 pty = yes | no (Unix only)
701 allocate a pseudoterminal for 'exec' option
702 redirect = [HOST:]PORT
704 redirect TLS client connections on certificate-based authentication
705 failures
706 This option only works in server mode. Some protocol negotiations
708 are also incompatible with the redirect option.
709 renegotiation = yes | no
711 support TLS renegotiation
712 Applications of the TLS renegotiation include some authentication
714 scenarios, or re-keying long lasting connections.
715 On the other hand this feature can facilitate a trivial CPU-
717 exhaustion DoS attack:
718 http://vincent.bernat.im/en/blog/2011-ssl-dos-mitigation.html
720 Please note that disabling TLS renegotiation does not fully
722 mitigate this issue.
723 default: yes (if supported by OpenSSL)
725 reset = yes | no
727 attempt to use the TCP RST flag to indicate an error
728 This option is not supported on some platforms.
730 default: yes
732 retry = yes | no
734 reconnect a connect+exec section after it was disconnected
735 default: no
737 requireCert = yes | no
739 require a client certificate for verifyChain or verifyPeer
740 With requireCert set to no, the stunnel server accepts client
742 connections that did not present a certificate.
743 Both verifyChain = yes and verifyPeer = yes imply requireCert =
745 yes.
746 default: no
748 setgid = GROUP (Unix only)
750 Unix group id
751 As a global option: setgid() to the specified group in daemon mode
753 and clear all other groups.
754 As a service-level option: set the group of the Unix socket
756 specified with "accept".
757 setuid = USER (Unix only)
759 Unix user id
760 As a global option: setuid() to the specified user in daemon mode.
762 As a service-level option: set the owner of the Unix socket
764 specified with "accept".
765 sessionCacheSize = NUM_ENTRIES
767 session cache size
768 sessionCacheSize specifies the maximum number of the internal
770 session cache entries.
771 The value of 0 can be used for unlimited size. It is not
773 recommended for production use due to the risk of a memory
774 exhaustion DoS attack.
775 sessionCacheTimeout = TIMEOUT
777 session cache timeout
778 This is the number of seconds to keep cached TLS sessions.
780 sessiond = HOST:PORT
782 address of sessiond TLS cache server
783 sni = SERVICE_NAME:SERVER_NAME_PATTERN (server mode)
785 Use the service as a slave service (a name-based virtual server)
786 for Server Name Indication TLS extension (RFC 3546).
787 SERVICE_NAME specifies the master service that accepts client
789 connections with the accept option. SERVER_NAME_PATTERN specifies
790 the host name to be redirected. The pattern may start with the '*'
791 character, e.g. '*.example.com'. Multiple slave services are
792 normally specified for a single master service. The sni option can
793 also be specified more than once within a single slave service.
794 This service, as well as the master service, may not be configured
796 in client mode.
797 The connect option of the slave service is ignored when the
799 protocol option is specified, as protocol connects to the remote
800 host before TLS handshake.
801 Libwrap checks (Unix only) are performed twice: with the master
803 service name after TCP connection is accepted, and with the slave
804 service name during the TLS handshake.
805 The sni option is only available when compiled with OpenSSL 1.0.0
807 and later.
808 sni = SERVER_NAME (client mode)
810 Use the parameter as the value of TLS Server Name Indication (RFC
811 3546) extension.
812 Empty SERVER_NAME disables sending the SNI extension.
814 The sni option is only available when compiled with OpenSSL 1.0.0
816 and later.
817 socket = a|l|r:OPTION=VALUE[:VALUE]
819 Set an option on the accept/local/remote socket
820 The values for the linger option are l_onof:l_linger. The values
822 for the time are tv_sec:tv_usec.
823 Examples:
825 socket = l:SO_LINGER=1:60
827 set one minute timeout for closing local socket
828 socket = r:SO_OOBINLINE=yes
829 place out-of-band data directly into the
830 receive data stream for remote sockets
831 socket = a:SO_REUSEADDR=no
832 disable address reuse (enabled by default)
833 socket = a:SO_BINDTODEVICE=lo
834 only accept connections on loopback interface
835 sslVersion = SSL_VERSION
837 select the TLS protocol version
838 Supported versions: all, SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2
840 sslVersion is obsolete and it will be removed in future releases of
842 stunnel. Use the following options instead:
843 options = NO_SSLv2
845 options = NO_SSLv3
846 options = NO_TLSv1
847 options = NO_TLSv1.1
848 options = NO_TLSv1.2
849 options = NO_TLSv1.3
850 Availability of specific protocols depends on the linked OpenSSL
852 library. Older versions of OpenSSL do not support TLSv1.1 and
853 TLSv1.2. Newer versions of OpenSSL do not support SSLv2.
854 Obsolete SSLv2 and SSLv3 are currently disabled by default. See
856 the options option documentation for details.
857 stack = BYTES (except for FORK model)
859 thread stack size
860 TIMEOUTbusy = SECONDS
862 time to wait for expected data
863 TIMEOUTclose = SECONDS
865 time to wait for close_notify (set to 0 for buggy MSIE)
866 TIMEOUTconnect = SECONDS
868 time to wait to connect to a remote host
869 TIMEOUTidle = SECONDS
871 time to keep an idle connection
872 transparent = none | source | destination | both (Unix only)
874 enable transparent proxy support on selected platforms
875 Supported values:
877 none
879 Disable transparent proxy support. This is the default.
880 source
882 Re-write the address to appear as if a wrapped daemon is
883 connecting from the TLS client machine instead of the machine
884 running stunnel.
885 This option is currently available in:
887 Remote mode (connect option) on Linux >=2.6.28
889 This configuration requires stunnel to be executed as root
890 and without the setuid option.
891 This configuration requires the following setup for
893 iptables and routing (possibly in /etc/rc.local or
894 equivalent file):
895 iptables -t mangle -N DIVERT
897 iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
898 iptables -t mangle -A DIVERT -j MARK --set-mark 1
899 iptables -t mangle -A DIVERT -j ACCEPT
900 ip rule add fwmark 1 lookup 100
901 ip route add local 0.0.0.0/0 dev lo table 100
902 echo 0 >/proc/sys/net/ipv4/conf/lo/rp_filter
903 stunnel must also to be executed as root and without the
905 setuid option.
906 Remote mode (connect option) on Linux 2.2.x
908 This configuration requires the kernel to be compiled with
909 the transparent proxy option. Connected service must be
910 installed on a separate host. Routing towards the clients
911 has to go through the stunnel box.
912 stunnel must also to be executed as root and without the
914 setuid option.
915 Remote mode (connect option) on FreeBSD >=8.0
917 This configuration requires additional firewall and routing
918 setup. stunnel must also to be executed as root and
919 without the setuid option.
920 Local mode (exec option)
922 This configuration works by pre-loading the libstunnel.so
923 shared library. _RLD_LIST environment variable is used on
924 Tru64, and LD_PRELOAD variable on other platforms.
925 destination
927 The original destination is used instead of the connect option.
928 A service section for transparent destination may look like
930 this:
931 [transparent]
933 client = yes
934 accept = <stunnel_port>
935 transparent = destination
936 This configuration requires iptables setup to work, possibly in
938 /etc/rc.local or equivalent file.
939 For a connect target installed on the same host:
941 /sbin/iptables -t nat -I OUTPUT -p tcp --dport <redirected_port> \
943 -m ! --uid-owner <stunnel_user_id> \
944 -j DNAT --to-destination <local_ip>:<stunnel_port>
945 For a connect target installed on a remote host:
947 /sbin/iptables -I INPUT -i eth0 -p tcp --dport <stunnel_port> -j ACCEPT
949 /sbin/iptables -t nat -I PREROUTING -p tcp --dport <redirected_port> \
950 -i eth0 -j DNAT --to-destination <local_ip>:<stunnel_port>
951 The transparent destination option is currently only supported
953 on Linux.
954 both
956 Use both source and destination transparent proxy.
957 Two legacy options are also supported for backward compatibility:
959 yes This option has been renamed to source.
961 no This option has been renamed to none.
963 verify = LEVEL
965 verify the peer certificate
966 This option is obsolete and should be replaced with the verifyChain
968 and verifyPeer options.
969 level 0
971 Request and ignore the peer certificate.
972 level 1
974 Verify the peer certificate if present.
975 level 2
977 Verify the peer certificate.
978 level 3
980 Verify the peer against a locally installed certificate.
981 level 4
983 Ignore the chain and only verify the peer certificate.
984 default
986 No verify.
987 verifyChain = yes | no
989 verify the peer certificate chain starting from the root CA
990 For server certificate verification it is essential to also require
992 a specific certificate with checkHost or checkIP.
993 The self-signed root CA certificate needs to be stored either in
995 the file specified with CAfile, or in the directory specified with
996 CApath.
997 default: no
999 verifyPeer = yes | no
1001 verify the peer certificate
1002 The peer certificate needs to be stored either in the file
1004 specified with CAfile, or in the directory specified with CApath.
1005 default: no
1007
1009 stunnel returns zero on success, non-zero on error.
1010
1012 The following signals can be used to control stunnel in Unix
1013 environment:
1014 SIGHUP
1016 Force a reload of the configuration file.
1017 Some global options will not be reloaded:
1019 · chroot
1021 · foreground
1023 · pid
1025 · setgid
1027 · setuid
1029 The use of the 'setuid' option will also prevent stunnel from
1031 binding to privileged (<1024) ports during configuration reloading.
1032 When the 'chroot' option is used, stunnel will look for all its
1034 files (including the configuration file, certificates, the log file
1035 and the pid file) within the chroot jail.
1036 SIGUSR1
1038 Close and reopen the stunnel log file. This function can be used
1039 for log rotation.
1040 SIGTERM, SIGQUIT, SIGINT
1042 Shut stunnel down.
1043 The result of sending any other signals to the server is undefined.
1045
1047 In order to provide TLS encapsulation to your local imapd service, use:
1048 [imapd]
1050 accept = 993
1051 exec = /usr/sbin/imapd
1052 execArgs = imapd
1053 or in remote mode:
1055 [imapd]
1057 accept = 993
1058 connect = 143
1059 In order to let your local e-mail client connect to a TLS-enabled imapd
1061 service on another server, configure the e-mail client to connect to
1062 localhost on port 119 and use:
1063 [imap]
1065 client = yes
1066 accept = 143
1067 connect = servername:993
1068 If you want to provide tunneling to your pppd daemon on port 2020, use
1070 something like:
1071 [vpn]
1073 accept = 2020
1074 exec = /usr/sbin/pppd
1075 execArgs = pppd local
1076 pty = yes
1077 If you want to use stunnel in inetd mode to launch your imapd process,
1079 you'd use this stunnel.conf. Note there must be no [service_name]
1080 section.
1081 exec = /usr/sbin/imapd
1083 execArgs = imapd
1084 To setup SOCKS VPN configure the following client service:
1086 [socks_client]
1088 client = yes
1089 accept = 127.0.0.1:1080
1090 connect = vpn_server:9080
1091 verifyPeer = yes
1092 CAfile = stunnel.pem
1093 The corresponding configuration on the vpn_server host:
1095 [socks_server]
1097 protocol = socks
1098 accept = 9080
1099 cert = stunnel.pem
1100 key = stunnel.key
1101 Now test your configuration on the client machine with:
1103 curl --socks4a localhost http://www.example.com/
1105 An example server mode SNI configuration:
1107 [virtual]
1109 ; master service
1110 accept = 443
1111 cert = default.pem
1112 connect = default.internal.mydomain.com:8080
1113 [sni1]
1115 ; slave service 1
1116 sni = virtual:server1.mydomain.com
1117 cert = server1.pem
1118 connect = server1.internal.mydomain.com:8081
1119 [sni2]
1121 ; slave service 2
1122 sni = virtual:server2.mydomain.com
1123 cert = server2.pem
1124 connect = server2.internal.mydomain.com:8082
1125 verifyPeer = yes
1126 CAfile = server2-allowed-clients.pem
1127 An example of advanced engine configuration allows for authentication
1129 with private keys stored in the Windows certificate store (Windows
1130 only). With the CAPI engine you don't need to manually select the
1131 client key to use. The client key is automatically selected based on
1132 the list of CAs trusted by the server.
1133 engine = capi
1135 [service]
1137 engineId = capi
1138 client = yes
1139 accept = 127.0.0.1:8080
1140 connect = example.com:8443
1141 An example of advanced engine configuration to use the certificate and
1143 the corresponding private key from a pkcs11 engine:
1144 engine = pkcs11
1146 engineCtrl = MODULE_PATH:opensc-pkcs11.so
1147 engineCtrl = PIN:123456
1148 [service]
1150 engineId = pkcs11
1151 client = yes
1152 accept = 127.0.0.1:8080
1153 connect = example.com:843
1154 cert = pkcs11:token=MyToken;object=MyCert
1155 key = pkcs11:token=MyToken;object=MyKey
1156 An example of advanced engine configuration to use the certificate and
1158 the corresponding private key from a SoftHSM token:
1159 engine = pkcs11
1161 engineCtrl = MODULE_PATH:softhsm2.dll
1162 engineCtrl = PIN:12345
1163 [service]
1165 engineId = pkcs11
1166 client = yes
1167 accept = 127.0.0.1:8080
1168 connect = example.com:843
1169 cert = pkcs11:token=MyToken;object=KeyCert
1170
1172 RESTRICTIONS
1173 stunnel cannot be used for the FTP daemon because of the nature of the
1174 FTP protocol which utilizes multiple ports for data transfers. There
1175 are available TLS-enabled versions of FTP and telnet daemons, however.
1176 INETD MODE
1178 The most common use of stunnel is to listen on a network port and
1179 establish communication with either a new port via the connect option,
1180 or a new program via the exec option. However there is a special case
1181 when you wish to have some other program accept incoming connections
1182 and launch stunnel, for example with inetd, xinetd, or tcpserver.
1183 For example, if you have the following line in inetd.conf:
1185 imaps stream tcp nowait root /usr/bin/stunnel stunnel /etc/stunnel/imaps.conf
1187 In these cases, the inetd-style program is responsible for binding a
1189 network socket (imaps above) and handing it to stunnel when a
1190 connection is received. Thus you do not want stunnel to have any
1191 accept option. All the Service Level Options should be placed in the
1192 global options section, and no [service_name] section will be present.
1193 See the EXAMPLES section for example configurations.
1194 CERTIFICATES
1196 Each TLS-enabled daemon needs to present a valid X.509 certificate to
1197 the peer. It also needs a private key to decrypt the incoming data. The
1198 easiest way to obtain a certificate and a key is to generate them with
1199 the free OpenSSL package. You can find more information on certificates
1200 generation on pages listed below.
1201 The order of contents of the .pem file is important. It should contain
1203 the unencrypted private key first, then a signed certificate (not
1204 certificate request). There should also be empty lines after the
1205 certificate and the private key. Any plaintext certificate information
1206 appended on the top of generated certificate should be discarded. So
1207 the file should look like this:
1208 -----BEGIN RSA PRIVATE KEY-----
1210 [encoded key]
1211 -----END RSA PRIVATE KEY-----
1212 [empty line]
1213 -----BEGIN CERTIFICATE-----
1214 [encoded certificate]
1215 -----END CERTIFICATE-----
1216 [empty line]
1217 RANDOMNESS
1219 stunnel needs to seed the PRNG (pseudo-random number generator) in
1220 order for TLS to use good randomness. The following sources are loaded
1221 in order until sufficient random data has been gathered:
1222 · The file specified with the RNDfile flag.
1224 · The file specified by the RANDFILE environment variable, if set.
1226 · The file .rnd in your home directory, if RANDFILE not set.
1228 · The file specified with '--with-random' at compile time.
1230 · The contents of the screen if running on Windows.
1232 · The egd socket specified with the EGD flag.
1234 · The egd socket specified with '--with-egd-sock' at compile time.
1236 · The /dev/urandom device.
1238 Note that on Windows machines that do not have console user interaction
1240 (mouse movements, creating windows, etc.) the screen contents are not
1241 variable enough to be sufficient, and you should provide a random file
1242 for use with the RNDfile flag.
1243 Note that the file specified with the RNDfile flag should contain
1245 random data -- that means it should contain different information each
1246 time stunnel is run. This is handled automatically unless the
1247 RNDoverwrite flag is used. If you wish to update this file manually,
1248 the openssl rand command in recent versions of OpenSSL, would be
1249 useful.
1250 Important note: If /dev/urandom is available, OpenSSL often seeds the
1252 PRNG with it while checking the random state. On systems with
1253 /dev/urandom OpenSSL is likely to use it even though it is listed at
1254 the very bottom of the list above. This is the behaviour of OpenSSL
1255 and not stunnel.
1256 DH PARAMETERS
1258 stunnel 4.40 and later contains hardcoded 2048-bit DH parameters.
1259 Starting with stunnel 5.18, these hardcoded DH parameters are replaced
1260 every 24 hours with autogenerated temporary DH parameters. DH
1261 parameter generation may take several minutes.
1262 Alternatively, it is possible to specify static DH parameters in the
1264 certificate file, which disables generating temporary DH parameters:
1265 openssl dhparam 2048 >> stunnel.pem
1267
1269 @sysconfdir@/stunnel/stunnel.conf
1270 stunnel configuration file
1271
1273 The execArgs option and the Win32 command line do not support quoting.
1274
1276 tcpd(8)
1277 access control facility for internet services
1278 inetd(8)
1280 internet 'super-server'
1281 http://www.stunnel.org/
1283 stunnel homepage
1284 http://www.openssl.org/
1286 OpenSSL project website
1287
1289 Michał Trojnara
1290 <Michal.Trojnara@stunnel.org>
12915.48 2018.07.02 stunnel(8)