CVE-2026-19487

Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass. The prescan walks the subject for positions where the full pattern could match, and the engine tries it from the leftmost one recorded. A failing transition sets the failed flag, and a later successful transition does not clear it, so the prescan reads the stale flag as a failure and stops before it can record a candidate that starts earlier. It takes a subject where one candidate is recorded and a later character then forces a fallback through a fail link that succeeds. Example: "ABCDE" =~ m/ABCF|BCDE|C/; # matches C at offset 2, not BCDE "ABCDE" =~ m/ABCF|BCDE|C(G)/; # no match, BCDE missed An alternation like this can miss input it should match, or match it on the wrong branch, so an access or filtering decision made from the result can be wrong.

CVSS v3 5.3 MEDIUM

5.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact LOW

Scope UNCHANGED

References

Link	Resource
https://github.com/Perl/perl5/commit/1a21abacaf6f684928bae8baaa153733c8c238eb.patch
https://github.com/Perl/perl5/issues/22892
http://www.openwall.com/lists/oss-security/2026/08/13/8
https://github.com/Perl/perl5/issues/22892

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-13 16:17

Updated : 2026-08-28 15:42

NVD link : CVE-2026-19487

Mitre link : CVE-2026-19487

CVE.ORG link : CVE-2026-19487

JSON object : View

Products Affected

No product.

CWE

CWE-670

Always-Incorrect Control Flow Implementation

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