/ 
perl-5.43.5
⭐ Starred 2013 / perlcheat
Security Advisories (5)
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-2026-4176 (2026-03-29)

Perl versions from 5.9.4 before 5.40.4-RC1, from 5.41.0 before 5.42.2-RC1, from 5.43.0 before 5.43.9 contain a vulnerable version of Compress::Raw::Zlib. Compress::Raw::Zlib is included in the Perl package as a dual-life core module, and is vulnerable to CVE-2026-3381 due to a vendored version of zlib which has several vulnerabilities, including CVE-2026-27171. The bundled Compress::Raw::Zlib was updated to version 2.221 in Perl blead commit c75ae9cc164205e1b6d6dbd57bd2c65c8593fe94.

CVE-2026-15534 (2026-08-09)

Perl versions through 5.45.1 have out-of-bounds heap reads and writes during regular expression matching via an undersized superlinear cache in S_regmatch. The regex engine's superlinear cache holds one bit per subject position for each participating WHILEM node, so the bit count is the subject length plus one times the number of nodes. Nothing checks that product for positive overflow of the signed 32-bit count: a 286331153 byte subject matched against a pattern with 15 participating nodes stores the count as 14, leaving a two byte cache. The cache is then indexed from the real match position and node number, so reads go past the end of the allocation, and on failure CACHEsayNO sets a bit past it. A caller that matches an attacker controlled subject of this size against a pattern of this shape can crash the process or corrupt heap memory.

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

perlcheat - Perl 5 Cheat Sheet

DESCRIPTION

This 'cheat sheet' is a handy reference, meant for beginning Perl programmers. Not everything is mentioned, but 195 features may already be overwhelming.

The sheet

CONTEXTS  SIGILS  ref        ARRAYS        HASHES
void      $scalar SCALAR     @array        %hash
scalar    @array  ARRAY      @array[0, 2]  @hash{'a', 'b'}
list      %hash   HASH       $array[0]     $hash{'a'}
          &sub    CODE
          *glob   GLOB       SCALAR VALUES
                  FORMAT     number, string, ref, glob, undef
REFERENCES
\      reference       $$foo[1]       aka $foo->[1]
$@%&*  dereference     $$foo{bar}     aka $foo->{bar}
[]     anon. arrayref  ${$$foo[1]}[2] aka $foo->[1]->[2]
{}     anon. hashref   ${$$foo[1]}[2] aka $foo->[1][2]
\()    list of refs
                       SYNTAX
OPERATOR PRECEDENCE    foreach (LIST) { }     for (a;b;c) { }
->                     while   (e) { }        until (e)   { }
++ --                  if      (e) { } elsif (e) { } else { }
**                     unless  (e) { } elsif (e) { } else { }
! ~ \ u+ u-            given   (e) { when (e) {} default {} }
=~ !~
* / % x                 NUMBERS vs STRINGS  FALSE vs TRUE
+ - .                   =          =        undef, "", 0, "0"
<< >>                   +          .        anything else
named uops              == !=      eq ne
< > <= >= lt gt le ge   < > <= >=  lt gt le ge
== != <=> eq ne cmp ~~  <=>        cmp
&
| ^             REGEX MODIFIERS       REGEX METACHARS
&&              /i case insensitive   ^      string begin
|| //           /m line based ^$      $      str end (bfr \n)
.. ...          /s . includes \n      +      one or more
?:              /x /xx ign. wh.space  *      zero or more
= += last goto  /p preserve           ?      zero or one
, =>            /a ASCII    /aa safe  {3,7}  repeat in range
list ops        /l locale   /d  dual  |      alternation
not             /u Unicode            []     character class
and             /e evaluate /ee rpts  \b     boundary
or xor          /g global             \z     string end
                /o compile pat once   (p)    capture
DEBUG                                 (?:p)  no capture
-MO=Deparse     REGEX CHARCLASSES     (?#t)  comment
-MO=Terse       .   [^\n]             (?=p)  ZW pos ahead
-D##            \s  whitespace        (?!p)  ZW neg ahead
-d:Trace        \w  word chars        (?<=p) ZW pos behind \K
                \d  digits            (?<!p) ZW neg behind
CONFIGURATION   \pP named property    (?>p)  no backtrack
perl -V:ivsize  \h  horiz.wh.space    (?|p|p)branch reset
                \R  linebreak         (?<n>p)named capture
                \S \W \D \H negate    \g{n}  ref to named cap
                                      \K     keep left part
FUNCTION RETURN LISTS
stat      localtime    caller         SPECIAL VARIABLES
 0 dev    0 second      0 package     $_    default variable
 1 ino    1 minute      1 filename    $0    program name
 2 mode   2 hour        2 line        $/    input separator
 3 nlink  3 day         3 subroutine  $\    output separator
 4 uid    4 month-1     4 hasargs     $|    autoflush
 5 gid    5 year-1900   5 wantarray   $!    sys/libcall error
 6 rdev   6 weekday     6 evaltext    $@    eval error
 7 size   7 yearday     7 is_require  $$    process ID
 8 atime  8 is_dst      8 hints       $.    line number
 9 mtime                9 bitmask     @ARGV command line args
10 ctime               10 hinthash    @INC  include paths
11 blksz               3..10 only     @_    subroutine args
12 blcks               with EXPR      %ENV  environment

ACKNOWLEDGEMENTS

The first version of this document appeared on Perl Monks, where several people had useful suggestions. Thank you, Perl Monks.

A special thanks to Damian Conway, who didn't only suggest important changes, but also took the time to count the number of listed features and make a Raku version to show that Perl will stay Perl.

AUTHOR

Juerd Waalboer <#####@juerd.nl>, with the help of many Perl Monks.

SEE ALSO