Perl up to 5.43.9 Trie Perl_study_chunk branch incorrect regex

Summaryinfo

A vulnerability was found in Perl up to 5.43.9. It has been declared as critical. This issue affects the function Perl_study_chunk of the component Trie. Executing a manipulation of the argument branch can lead to incorrect regex. This vulnerability appears as CVE-2026-13221. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability classified as critical was found in Perl up to 5.43.9. This vulnerability affects the function Perl_study_chunk of the component Trie. The manipulation of the argument branch with an unknown input leads to a incorrect regex vulnerability. The CWE definition for the vulnerability is CWE-185. The product specifies a regular expression in a way that causes data to be improperly matched or compared. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability was named CVE-2026-13221 since 06/24/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 07/13/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Programming Language Software

Name

• Perl

Version

• 5.43.0
• 5.43.1
• 5.43.2
• 5.43.3
• 5.43.4
• 5.43.5
• 5.43.6
• 5.43.7
• 5.43.8
• 5.43.9

License

• open-source

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