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perl-5.42.2
⭐ Starred 2013 / strict
Security Advisories (3)
CVE-2026-13221 (2026-07-13)

Perl versions through 5.43.9 produce silently incorrect regular expression matches when an alternation of more than 65535 fixed string branches is compiled into a trie in Perl_study_chunk. When such branches are combined into a trie, the delta between the first branch and the shared tail is stored in a 16-bit field. A branch count above 65535 overflows the field, and the trie's match decision table is truncated with no warning or error. A pattern of this shape produces false positive matches (matching strings it should not) and false negative matches (failing to match strings it should). When such a pattern gates an access or filtering decision, the result is wrong.

CVE-2026-57432 (2026-07-13)

Perl versions through 5.43.10 have an integer overflow in S_measure_struct leading to an out-of-bounds heap read in pack and unpack. S_measure_struct adds each item's size times its repeat count to a running total with no overflow check, so a large repeat count in a pack or unpack template wraps the signed SSize_t total negative. The @, X, and x position codes then guard their moves with a signed length comparison that passes when the length is negative, advancing the buffer pointer out of bounds. A template derived from untrusted input can read heap memory past the buffer and return it to the caller.

CVE-2026-8376 (2026-05-25)

Perl versions through 5.43.10 have a heap buffer overflow when compiling regular expressions with a repeated fixed string on 32-bit builds. Perl_study_chunk in regcomp_study.c checked the size of the joined substring buffer in characters rather than bytes. For a quantified fixed substring with a large minimum count, the byte length mincount * l could overflow SSize_t, producing an undersized SvGROW allocation; the subsequent copy writes past the end of the buffer. A caller that compiles an attacker-controlled regular expression on a 32-bit perl build triggers a heap buffer overflow at compile time.

NAME

strict - Perl pragma to restrict unsafe constructs

SYNOPSIS

use strict;

use strict "vars";
use strict "refs";
use strict "subs";

use strict;
no strict "vars";

DESCRIPTION

The strict pragma disables certain Perl expressions that could behave unexpectedly or are difficult to debug, turning them into errors. The effect of this pragma is limited to the current file or scope block.

If no import list is supplied, all possible restrictions are assumed. (This is the safest mode to operate in, but is sometimes too strict for casual programming.) Currently, there are three possible things to be strict about: "subs", "vars", and "refs".

strict refs

This generates a runtime error if you use symbolic references (see perlref).

use strict 'refs';
$ref = \$foo;
print $$ref;	# ok
$ref = "foo";
print $$ref;	# runtime error; normally ok
$file = "STDOUT";
print $file "Hi!";	# error; note: no comma after $file

There is one exception to this rule:

$bar = \&{'foo'};
&$bar;

is allowed so that goto &$AUTOLOAD would not break under stricture.

strict vars

This generates a compile-time error if you access a variable that was neither explicitly declared (using any of my, our, state, or use vars) nor fully qualified. (Because this is to avoid variable suicide problems and subtle dynamic scoping issues, a merely local variable isn't good enough.) See "my" in perlfunc, "our" in perlfunc, "state" in perlfunc, "local" in perlfunc, and vars.

use strict 'vars';
$X::foo = 1;	 # ok, fully qualified
my $foo = 10;	 # ok, my() var
local $baz = 9;	 # blows up, $baz not declared before

package Cinna;
our $bar;			# Declares $bar in current package
$bar = 'HgS';		# ok, global declared via pragma

The local() generated a compile-time error because you just touched a global name without fully qualifying it.

Because of their special use by sort(), the variables $a and $b are exempted from this check.

strict subs

This disables the poetry optimization, generating a compile-time error if you try to use a bareword identifier that's not a subroutine, unless it is a simple identifier (no colons) and that it appears in curly braces, on the left hand side of the => symbol, or has the unary minus operator applied to it.

use strict 'subs';
$SIG{PIPE} = Plumber;   # blows up
$SIG{PIPE} = "Plumber"; # fine: quoted string is always ok
$SIG{PIPE} = \&Plumber; # preferred form

See "Pragmatic Modules" in perlmodlib.

HISTORY

strict 'subs', with Perl 5.6.1, erroneously permitted to use an unquoted compound identifier (e.g. Foo::Bar) as a hash key (before => or inside curlies), but without forcing it always to a literal string.

Starting with Perl 5.8.1 strict is strict about its restrictions: if unknown restrictions are used, the strict pragma will abort with

Unknown 'strict' tag(s) '...'

As of version 1.04 (Perl 5.10), strict verifies that it is used as "strict" to avoid the dreaded Strict trap on case insensitive file systems.

Beginning with Perl 5.12, use of "use VERSION" (where VERSION >= 5.11.0) now lexically enables strictures just like "use strict" (in addition to the normal "use VERSION" effects and features.) In other words, "use v5.011" or higher now implies "use strict" automatically, as noted in "Implicit strictures" in perl5120delta and use VERSION.