1PERLSEC(1) Perl Programmers Reference Guide PERLSEC(1)
2
6 perlsec - Perl security
7
9 Perl is designed to make it easy to program securely even when running
10 with extra privileges, like setuid or setgid programs. Unlike most
11 command line shells, which are based on multiple substitution passes on
12 each line of the script, Perl uses a more conventional evaluation
13 scheme with fewer hidden snags. Additionally, because the language has
14 more builtin functionality, it can rely less upon external (and
15 possibly untrustworthy) programs to accomplish its purposes.
16
18 If you believe you have found a security vulnerability in Perl, please
19 email the details to perl5-security-report@perl.org. This creates a new
20 Request Tracker ticket in a special queue which isn't initially
21 publicly accessible. The email will also be copied to a closed
22 subscription unarchived mailing list which includes all the core
23 committers, who will be able to help assess the impact of issues,
24 figure out a resolution, and help co-ordinate the release of patches to
25 mitigate or fix the problem across all platforms on which Perl is
26 supported. Please only use this address for security issues in the Perl
27 core, not for modules independently distributed on CPAN.
28 When sending an initial request to the security email address, please
30 don't Cc any other parties, because if they reply to all, the reply
31 will generate yet another new ticket. Once you have received an initial
32 reply with a "[perl #NNNNNN]" ticket number in the headline, it's okay
33 to Cc subsequent replies to third parties: all emails to the
34 perl5-security-report address with the ticket number in the subject
35 line will be added to the ticket; without it, a new ticket will be
36 created.
37
39 Taint mode
40 Perl automatically enables a set of special security checks, called
41 taint mode, when it detects its program running with differing real and
42 effective user or group IDs. The setuid bit in Unix permissions is
43 mode 04000, the setgid bit mode 02000; either or both may be set. You
44 can also enable taint mode explicitly by using the -T command line
45 flag. This flag is strongly suggested for server programs and any
46 program run on behalf of someone else, such as a CGI script. Once
47 taint mode is on, it's on for the remainder of your script.
48 While in this mode, Perl takes special precautions called taint checks
50 to prevent both obvious and subtle traps. Some of these checks are
51 reasonably simple, such as verifying that path directories aren't
52 writable by others; careful programmers have always used checks like
53 these. Other checks, however, are best supported by the language
54 itself, and it is these checks especially that contribute to making a
55 set-id Perl program more secure than the corresponding C program.
56 You may not use data derived from outside your program to affect
58 something else outside your program--at least, not by accident. All
59 command line arguments, environment variables, locale information (see
60 perllocale), results of certain system calls ("readdir()",
61 "readlink()", the variable of "shmread()", the messages returned by
62 "msgrcv()", the password, gcos and shell fields returned by the
63 "getpwxxx()" calls), and all file input are marked as "tainted".
64 Tainted data may not be used directly or indirectly in any command that
65 invokes a sub-shell, nor in any command that modifies files,
66 directories, or processes, with the following exceptions:
67 · Arguments to "print" and "syswrite" are not checked for
69 taintedness.
70 · Symbolic methods
72 $obj->$method(@args);
74 and symbolic sub references
76 &{$foo}(@args);
78 $foo->(@args);
79 are not checked for taintedness. This requires extra carefulness
81 unless you want external data to affect your control flow. Unless
82 you carefully limit what these symbolic values are, people are able
83 to call functions outside your Perl code, such as POSIX::system, in
84 which case they are able to run arbitrary external code.
85 · Hash keys are never tainted.
87 For efficiency reasons, Perl takes a conservative view of whether data
89 is tainted. If an expression contains tainted data, any subexpression
90 may be considered tainted, even if the value of the subexpression is
91 not itself affected by the tainted data.
92 Because taintedness is associated with each scalar value, some elements
94 of an array or hash can be tainted and others not. The keys of a hash
95 are never tainted.
96 For example:
98 $arg = shift; # $arg is tainted
100 $hid = $arg . 'bar'; # $hid is also tainted
101 $line = <>; # Tainted
102 $line = <STDIN>; # Also tainted
103 open FOO, "/home/me/bar" or die $!;
104 $line = <FOO>; # Still tainted
105 $path = $ENV{'PATH'}; # Tainted, but see below
106 $data = 'abc'; # Not tainted
107 system "echo $arg"; # Insecure
109 system "/bin/echo", $arg; # Considered insecure
110 # (Perl doesn't know about /bin/echo)
111 system "echo $hid"; # Insecure
112 system "echo $data"; # Insecure until PATH set
113 $path = $ENV{'PATH'}; # $path now tainted
115 $ENV{'PATH'} = '/bin:/usr/bin';
117 delete @ENV{'IFS', 'CDPATH', 'ENV', 'BASH_ENV'};
118 $path = $ENV{'PATH'}; # $path now NOT tainted
120 system "echo $data"; # Is secure now!
121 open(FOO, "< $arg"); # OK - read-only file
123 open(FOO, "> $arg"); # Not OK - trying to write
124 open(FOO,"echo $arg|"); # Not OK
126 open(FOO,"-|")
127 or exec 'echo', $arg; # Also not OK
128 $shout = `echo $arg`; # Insecure, $shout now tainted
130 unlink $data, $arg; # Insecure
132 umask $arg; # Insecure
133 exec "echo $arg"; # Insecure
135 exec "echo", $arg; # Insecure
136 exec "sh", '-c', $arg; # Very insecure!
137 @files = <*.c>; # insecure (uses readdir() or similar)
139 @files = glob('*.c'); # insecure (uses readdir() or similar)
140 # In either case, the results of glob are tainted, since the list of
142 # filenames comes from outside of the program.
143 $bad = ($arg, 23); # $bad will be tainted
145 $arg, `true`; # Insecure (although it isn't really)
146 If you try to do something insecure, you will get a fatal error saying
148 something like "Insecure dependency" or "Insecure $ENV{PATH}".
149 The exception to the principle of "one tainted value taints the whole
151 expression" is with the ternary conditional operator "?:". Since code
152 with a ternary conditional
153 $result = $tainted_value ? "Untainted" : "Also untainted";
155 is effectively
157 if ( $tainted_value ) {
159 $result = "Untainted";
160 } else {
161 $result = "Also untainted";
162 }
163 it doesn't make sense for $result to be tainted.
165 Laundering and Detecting Tainted Data
167 To test whether a variable contains tainted data, and whose use would
168 thus trigger an "Insecure dependency" message, you can use the
169 "tainted()" function of the Scalar::Util module, available in your
170 nearby CPAN mirror, and included in Perl starting from the release
171 5.8.0. Or you may be able to use the following "is_tainted()"
172 function.
173 sub is_tainted {
175 local $@; # Don't pollute caller's value.
176 return ! eval { eval("#" . substr(join("", @_), 0, 0)); 1 };
177 }
178 This function makes use of the fact that the presence of tainted data
180 anywhere within an expression renders the entire expression tainted.
181 It would be inefficient for every operator to test every argument for
182 taintedness. Instead, the slightly more efficient and conservative
183 approach is used that if any tainted value has been accessed within the
184 same expression, the whole expression is considered tainted.
185 But testing for taintedness gets you only so far. Sometimes you have
187 just to clear your data's taintedness. Values may be untainted by
188 using them as keys in a hash; otherwise the only way to bypass the
189 tainting mechanism is by referencing subpatterns from a regular
190 expression match. Perl presumes that if you reference a substring
191 using $1, $2, etc. in a non-tainting pattern, that you knew what you
192 were doing when you wrote that pattern. That means using a bit of
193 thought--don't just blindly untaint anything, or you defeat the entire
194 mechanism. It's better to verify that the variable has only good
195 characters (for certain values of "good") rather than checking whether
196 it has any bad characters. That's because it's far too easy to miss
197 bad characters that you never thought of.
198 Here's a test to make sure that the data contains nothing but "word"
200 characters (alphabetics, numerics, and underscores), a hyphen, an at
201 sign, or a dot.
202 if ($data =~ /^([-\@\w.]+)$/) {
204 $data = $1; # $data now untainted
205 } else {
206 die "Bad data in '$data'"; # log this somewhere
207 }
208 This is fairly secure because "/\w+/" doesn't normally match shell
210 metacharacters, nor are dot, dash, or at going to mean something
211 special to the shell. Use of "/.+/" would have been insecure in theory
212 because it lets everything through, but Perl doesn't check for that.
213 The lesson is that when untainting, you must be exceedingly careful
214 with your patterns. Laundering data using regular expression is the
215 only mechanism for untainting dirty data, unless you use the strategy
216 detailed below to fork a child of lesser privilege.
217 The example does not untaint $data if "use locale" is in effect,
219 because the characters matched by "\w" are determined by the locale.
220 Perl considers that locale definitions are untrustworthy because they
221 contain data from outside the program. If you are writing a locale-
222 aware program, and want to launder data with a regular expression
223 containing "\w", put "no locale" ahead of the expression in the same
224 block. See "SECURITY" in perllocale for further discussion and
225 examples.
226 Switches On the "#!" Line
228 When you make a script executable, in order to make it usable as a
229 command, the system will pass switches to perl from the script's #!
230 line. Perl checks that any command line switches given to a setuid (or
231 setgid) script actually match the ones set on the #! line. Some Unix
232 and Unix-like environments impose a one-switch limit on the #! line,
233 so you may need to use something like "-wU" instead of "-w -U" under
234 such systems. (This issue should arise only in Unix or Unix-like
235 environments that support #! and setuid or setgid scripts.)
236 Taint mode and @INC
238 When the taint mode ("-T") is in effect, the environment variables
239 "PERL5LIB" and "PERLLIB" are ignored by Perl. You can still adjust
240 @INC from outside the program by using the "-I" command line option as
241 explained in perlrun. The two environment variables are ignored
242 because they are obscured, and a user running a program could be
243 unaware that they are set, whereas the "-I" option is clearly visible
244 and therefore permitted.
245 Another way to modify @INC without modifying the program, is to use the
247 "lib" pragma, e.g.:
248 perl -Mlib=/foo program
250 The benefit of using "-Mlib=/foo" over "-I/foo", is that the former
252 will automagically remove any duplicated directories, while the latter
253 will not.
254 Note that if a tainted string is added to @INC, the following problem
256 will be reported:
257 Insecure dependency in require while running with -T switch
259 On versions of Perl before 5.26, activating taint mode will also remove
261 the current directory (".") from the default value of @INC. Since
262 version 5.26, the current directory isn't included in @INC by default.
263 Cleaning Up Your Path
265 For "Insecure $ENV{PATH}" messages, you need to set $ENV{'PATH'} to a
266 known value, and each directory in the path must be absolute and non-
267 writable by others than its owner and group. You may be surprised to
268 get this message even if the pathname to your executable is fully
269 qualified. This is not generated because you didn't supply a full path
270 to the program; instead, it's generated because you never set your PATH
271 environment variable, or you didn't set it to something that was safe.
272 Because Perl can't guarantee that the executable in question isn't
273 itself going to turn around and execute some other program that is
274 dependent on your PATH, it makes sure you set the PATH.
275 The PATH isn't the only environment variable which can cause problems.
277 Because some shells may use the variables IFS, CDPATH, ENV, and
278 BASH_ENV, Perl checks that those are either empty or untainted when
279 starting subprocesses. You may wish to add something like this to your
280 setid and taint-checking scripts.
281 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; # Make %ENV safer
283 It's also possible to get into trouble with other operations that don't
285 care whether they use tainted values. Make judicious use of the file
286 tests in dealing with any user-supplied filenames. When possible, do
287 opens and such after properly dropping any special user (or group!)
288 privileges. Perl doesn't prevent you from opening tainted filenames
289 for reading, so be careful what you print out. The tainting mechanism
290 is intended to prevent stupid mistakes, not to remove the need for
291 thought.
292 Perl does not call the shell to expand wild cards when you pass
294 "system" and "exec" explicit parameter lists instead of strings with
295 possible shell wildcards in them. Unfortunately, the "open", "glob",
296 and backtick functions provide no such alternate calling convention, so
297 more subterfuge will be required.
298 Perl provides a reasonably safe way to open a file or pipe from a
300 setuid or setgid program: just create a child process with reduced
301 privilege who does the dirty work for you. First, fork a child using
302 the special "open" syntax that connects the parent and child by a pipe.
303 Now the child resets its ID set and any other per-process attributes,
304 like environment variables, umasks, current working directories, back
305 to the originals or known safe values. Then the child process, which
306 no longer has any special permissions, does the "open" or other system
307 call. Finally, the child passes the data it managed to access back to
308 the parent. Because the file or pipe was opened in the child while
309 running under less privilege than the parent, it's not apt to be
310 tricked into doing something it shouldn't.
311 Here's a way to do backticks reasonably safely. Notice how the "exec"
313 is not called with a string that the shell could expand. This is by
314 far the best way to call something that might be subjected to shell
315 escapes: just never call the shell at all.
316 use English;
318 die "Can't fork: $!" unless defined($pid = open(KID, "-|"));
319 if ($pid) { # parent
320 while (<KID>) {
321 # do something
322 }
323 close KID;
324 } else {
325 my @temp = ($EUID, $EGID);
326 my $orig_uid = $UID;
327 my $orig_gid = $GID;
328 $EUID = $UID;
329 $EGID = $GID;
330 # Drop privileges
331 $UID = $orig_uid;
332 $GID = $orig_gid;
333 # Make sure privs are really gone
334 ($EUID, $EGID) = @temp;
335 die "Can't drop privileges"
336 unless $UID == $EUID && $GID eq $EGID;
337 $ENV{PATH} = "/bin:/usr/bin"; # Minimal PATH.
338 # Consider sanitizing the environment even more.
339 exec 'myprog', 'arg1', 'arg2'
340 or die "can't exec myprog: $!";
341 }
342 A similar strategy would work for wildcard expansion via "glob",
344 although you can use "readdir" instead.
345 Taint checking is most useful when although you trust yourself not to
347 have written a program to give away the farm, you don't necessarily
348 trust those who end up using it not to try to trick it into doing
349 something bad. This is the kind of security checking that's useful for
350 set-id programs and programs launched on someone else's behalf, like
351 CGI programs.
352 This is quite different, however, from not even trusting the writer of
354 the code not to try to do something evil. That's the kind of trust
355 needed when someone hands you a program you've never seen before and
356 says, "Here, run this." For that kind of safety, you might want to
357 check out the Safe module, included standard in the Perl distribution.
358 This module allows the programmer to set up special compartments in
359 which all system operations are trapped and namespace access is
360 carefully controlled. Safe should not be considered bullet-proof,
361 though: it will not prevent the foreign code to set up infinite loops,
362 allocate gigabytes of memory, or even abusing perl bugs to make the
363 host interpreter crash or behave in unpredictable ways. In any case
364 it's better avoided completely if you're really concerned about
365 security.
366 Shebang Race Condition
368 Beyond the obvious problems that stem from giving special privileges to
369 systems as flexible as scripts, on many versions of Unix, set-id
370 scripts are inherently insecure right from the start. The problem is a
371 race condition in the kernel. Between the time the kernel opens the
372 file to see which interpreter to run and when the (now-set-id)
373 interpreter turns around and reopens the file to interpret it, the file
374 in question may have changed, especially if you have symbolic links on
375 your system.
376 Some Unixes, especially more recent ones, are free of this inherent
378 security bug. On such systems, when the kernel passes the name of the
379 set-id script to open to the interpreter, rather than using a pathname
380 subject to meddling, it instead passes /dev/fd/3. This is a special
381 file already opened on the script, so that there can be no race
382 condition for evil scripts to exploit. On these systems, Perl should
383 be compiled with "-DSETUID_SCRIPTS_ARE_SECURE_NOW". The Configure
384 program that builds Perl tries to figure this out for itself, so you
385 should never have to specify this yourself. Most modern releases of
386 SysVr4 and BSD 4.4 use this approach to avoid the kernel race
387 condition.
388 If you don't have the safe version of set-id scripts, all is not lost.
390 Sometimes this kernel "feature" can be disabled, so that the kernel
391 either doesn't run set-id scripts with the set-id or doesn't run them
392 at all. Either way avoids the exploitability of the race condition,
393 but doesn't help in actually running scripts set-id.
394 If the kernel set-id script feature isn't disabled, then any set-id
396 script provides an exploitable vulnerability. Perl can't avoid being
397 exploitable, but will point out vulnerable scripts where it can. If
398 Perl detects that it is being applied to a set-id script then it will
399 complain loudly that your set-id script is insecure, and won't run it.
400 When Perl complains, you need to remove the set-id bit from the script
401 to eliminate the vulnerability. Refusing to run the script doesn't in
402 itself close the vulnerability; it is just Perl's way of encouraging
403 you to do this.
404 To actually run a script set-id, if you don't have the safe version of
406 set-id scripts, you'll need to put a C wrapper around the script. A C
407 wrapper is just a compiled program that does nothing except call your
408 Perl program. Compiled programs are not subject to the kernel bug
409 that plagues set-id scripts. Here's a simple wrapper, written in C:
410 #include <unistd.h>
412 #include <stdio.h>
413 #include <string.h>
414 #include <errno.h>
415 #define REAL_PATH "/path/to/script"
417 int main(int argc, char **argv)
419 {
420 execv(REAL_PATH, argv);
421 fprintf(stderr, "%s: %s: %s\n",
422 argv[0], REAL_PATH, strerror(errno));
423 return 127;
424 }
425 Compile this wrapper into a binary executable and then make it rather
427 than your script setuid or setgid. Note that this wrapper isn't doing
428 anything to sanitise the execution environment other than ensuring that
429 a safe path to the script is used. It only avoids the shebang race
430 condition. It relies on Perl's own features, and on the script itself
431 being careful, to make it safe enough to run the script set-id.
432 Protecting Your Programs
434 There are a number of ways to hide the source to your Perl programs,
435 with varying levels of "security".
436 First of all, however, you can't take away read permission, because the
438 source code has to be readable in order to be compiled and interpreted.
439 (That doesn't mean that a CGI script's source is readable by people on
440 the web, though.) So you have to leave the permissions at the socially
441 friendly 0755 level. This lets people on your local system only see
442 your source.
443 Some people mistakenly regard this as a security problem. If your
445 program does insecure things, and relies on people not knowing how to
446 exploit those insecurities, it is not secure. It is often possible for
447 someone to determine the insecure things and exploit them without
448 viewing the source. Security through obscurity, the name for hiding
449 your bugs instead of fixing them, is little security indeed.
450 You can try using encryption via source filters (Filter::* from CPAN,
452 or Filter::Util::Call and Filter::Simple since Perl 5.8). But crackers
453 might be able to decrypt it. You can try using the byte code compiler
454 and interpreter described below, but crackers might be able to de-
455 compile it. You can try using the native-code compiler described
456 below, but crackers might be able to disassemble it. These pose
457 varying degrees of difficulty to people wanting to get at your code,
458 but none can definitively conceal it (this is true of every language,
459 not just Perl).
460 If you're concerned about people profiting from your code, then the
462 bottom line is that nothing but a restrictive license will give you
463 legal security. License your software and pepper it with threatening
464 statements like "This is unpublished proprietary software of XYZ Corp.
465 Your access to it does not give you permission to use it blah blah
466 blah." You should see a lawyer to be sure your license's wording will
467 stand up in court.
468 Unicode
470 Unicode is a new and complex technology and one may easily overlook
471 certain security pitfalls. See perluniintro for an overview and
472 perlunicode for details, and "Security Implications of Unicode" in
473 perlunicode for security implications in particular.
474 Algorithmic Complexity Attacks
476 Certain internal algorithms used in the implementation of Perl can be
477 attacked by choosing the input carefully to consume large amounts of
478 either time or space or both. This can lead into the so-called Denial
479 of Service (DoS) attacks.
480 · Hash Algorithm - Hash algorithms like the one used in Perl are well
482 known to be vulnerable to collision attacks on their hash function.
483 Such attacks involve constructing a set of keys which collide into
484 the same bucket producing inefficient behavior. Such attacks often
485 depend on discovering the seed of the hash function used to map the
486 keys to buckets. That seed is then used to brute-force a key set
487 which can be used to mount a denial of service attack. In Perl
488 5.8.1 changes were introduced to harden Perl to such attacks, and
489 then later in Perl 5.18.0 these features were enhanced and
490 additional protections added.
491 At the time of this writing, Perl 5.18.0 is considered to be well-
493 hardened against algorithmic complexity attacks on its hash
494 implementation. This is largely owed to the following measures
495 mitigate attacks:
496 Hash Seed Randomization
498 In order to make it impossible to know what seed to generate an
499 attack key set for, this seed is randomly initialized at
500 process start. This may be overridden by using the
501 PERL_HASH_SEED environment variable, see "PERL_HASH_SEED" in
502 perlrun. This environment variable controls how items are
503 actually stored, not how they are presented via "keys",
504 "values" and "each".
505 Hash Traversal Randomization
507 Independent of which seed is used in the hash function, "keys",
508 "values", and "each" return items in a per-hash randomized
509 order. Modifying a hash by insertion will change the iteration
510 order of that hash. This behavior can be overridden by using
511 "hash_traversal_mask()" from Hash::Util or by using the
512 PERL_PERTURB_KEYS environment variable, see "PERL_PERTURB_KEYS"
513 in perlrun. Note that this feature controls the "visible"
514 order of the keys, and not the actual order they are stored in.
515 Bucket Order Perturbance
517 When items collide into a given hash bucket the order they are
518 stored in the chain is no longer predictable in Perl 5.18.
519 This has the intention to make it harder to observe a
520 collision. This behavior can be overridden by using the
521 PERL_PERTURB_KEYS environment variable, see "PERL_PERTURB_KEYS"
522 in perlrun.
523 New Default Hash Function
525 The default hash function has been modified with the intention
526 of making it harder to infer the hash seed.
527 Alternative Hash Functions
529 The source code includes multiple hash algorithms to choose
530 from. While we believe that the default perl hash is robust to
531 attack, we have included the hash function Siphash as a fall-
532 back option. At the time of release of Perl 5.18.0 Siphash is
533 believed to be of cryptographic strength. This is not the
534 default as it is much slower than the default hash.
535 Without compiling a special Perl, there is no way to get the exact
537 same behavior of any versions prior to Perl 5.18.0. The closest
538 one can get is by setting PERL_PERTURB_KEYS to 0 and setting the
539 PERL_HASH_SEED to a known value. We do not advise those settings
540 for production use due to the above security considerations.
541 Perl has never guaranteed any ordering of the hash keys, and the
543 ordering has already changed several times during the lifetime of
544 Perl 5. Also, the ordering of hash keys has always been, and
545 continues to be, affected by the insertion order and the history of
546 changes made to the hash over its lifetime.
547 Also note that while the order of the hash elements might be
549 randomized, this "pseudo-ordering" should not be used for
550 applications like shuffling a list randomly (use
551 "List::Util::shuffle()" for that, see List::Util, a standard core
552 module since Perl 5.8.0; or the CPAN module
553 "Algorithm::Numerical::Shuffle"), or for generating permutations
554 (use e.g. the CPAN modules "Algorithm::Permute" or
555 "Algorithm::FastPermute"), or for any cryptographic applications.
556 Tied hashes may have their own ordering and algorithmic complexity
558 attacks.
559 · Regular expressions - Perl's regular expression engine is so called
561 NFA (Non-deterministic Finite Automaton), which among other things
562 means that it can rather easily consume large amounts of both time
563 and space if the regular expression may match in several ways.
564 Careful crafting of the regular expressions can help but quite
565 often there really isn't much one can do (the book "Mastering
566 Regular Expressions" is required reading, see perlfaq2). Running
567 out of space manifests itself by Perl running out of memory.
568 · Sorting - the quicksort algorithm used in Perls before 5.8.0 to
570 implement the sort() function was very easy to trick into
571 misbehaving so that it consumes a lot of time. Starting from Perl
572 5.8.0 a different sorting algorithm, mergesort, is used by default.
573 Mergesort cannot misbehave on any input.
574 See
576 <https://www.usenix.org/legacy/events/sec03/tech/full_papers/crosby/crosby.pdf>
577 for more information, and any computer science textbook on algorithmic
578 complexity.
579 Using Sudo
581 The popular tool "sudo" provides a controlled way for users to be able
582 to run programs as other users. It sanitises the execution environment
583 to some extent, and will avoid the shebang race condition. If you
584 don't have the safe version of set-id scripts, then "sudo" may be a
585 more convenient way of executing a script as another user than writing
586 a C wrapper would be.
587 However, "sudo" sets the real user or group ID to that of the target
589 identity, not just the effective ID as set-id bits do. As a result,
590 Perl can't detect that it is running under "sudo", and so won't
591 automatically take its own security precautions such as turning on
592 taint mode. Where "sudo" configuration dictates exactly which command
593 can be run, the approved command may include a "-T" option to perl to
594 enable taint mode.
595 In general, it is necessary to evaluate the suitaility of a script to
597 run under "sudo" specifically with that kind of execution environment
598 in mind. It is neither necessary nor sufficient for the same script to
599 be suitable to run in a traditional set-id arrangement, though many of
600 the issues overlap.
601
603 perlrun for its description of cleaning up environment variables.
604perl v5.30.2 2020-03-27 PERLSEC(1)