USN-8736-1: Perl vulnerabilities

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.

Perl versions from 5.9.4 before 5.41.9 can produce incorrect regular-expression match results because a stale failure flag in the Aho-Corasick prescan (S_find_byclass) is not cleared when a later transition succeeds, causing the prescan to stop before it records an earlier valid match position. The flaw is triggered by alternation patterns where one candidate position is recorded and a later character then forces a fallback through a fail link that succeeds; for example, 'ABCDE' =~ m/ABCF|BCDE|C/ matches C at offset 2 instead of BCDE, and m/ABCF|BCDE|C(G/) fails to match at all. An attacker who controls input to such a regex can make an access-control, validation, or filtering decision resolve incorrectly, either matching the wrong alternative branch or missing a match entirely, with impact rated low (CVSS 5.3, medium). Any application running an affected Perl interpreter whose security-relevant regexes use alternations is exposed, and because Perl ships by default with virtually all Linux and Unix systems the installed base is enormous even though only specific pattern shapes trigger the bug. No public proof-of-concept is known, the issue is not in CISA KEV, and EPSS puts the 30-day exploitation probability at 0.4%, so no exploitation is currently known.

Do: Upgrade to Perl 5.41.9 or later, or apply vendor backports such as Ubuntu's USN-8736-1 for affected distribution packages. Audit regex-based access-control, validation, and filtering rules that use alternations, and test them against inputs where a later alternative should match after an earlier one fails. No reliable workaround exists because the defect is inside the regex engine itself, so patching is the primary remediation.