SEPTEMBER 13, 2026
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Case File

CVE-2026-13221

CRITICAL · CVSS 9.1 EPSS 0.43% Public Exploit

Source: NVD + CISA KEV + EPSS · Published 2026-07-13 · Last synced 2026-08-12

CyberRota Analysis

AI-Generated

Perl versions up to 5.43.9 are vulnerable to a critical flaw that causes incorrect regular expression matches when more than 65,535 fixed string branches are compiled into a trie, leading to silent truncation of the match decision table. This vulnerability can result in false positives and negatives, potentially compromising access control and filtering mechanisms. Organizations utilizing Perl for applications that rely on complex regular expressions should prioritize addressing this issue to mitigate security risks.

Public Exploit Signal

A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.

Note: these links are listed for security research and verification purposes only.

CVE
CVE-2026-13221
Severity
CRITICAL
CVSS
9.1
EPSS
0.43%

Original NVD Description

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.

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