Incorrect regex decisions via 16-bit trie overflow
Published Jul 13, 2026 · Updated Jul 13, 2026
Regular expression logic error in Perl 5.43.9 and earlier allows remote attackers to cause incorrect matches via crafted patterns. The Perl_study_chunk trie compiler stores the delta from the first branch to the shared tail in a 16-bit field, which wraps above 65,535 branches and truncates the decision table. Reachability requires an application to compile an attacker-influenced alternation exceeding 65,535 fixed strings; affected decisions can admit denied input or reject allowed input.
Summary
What happened
Regular expression logic error in Perl 5.43.9 and earlier allows remote attackers to cause incorrect matches via crafted patterns. The Perl_study_chunk trie compiler stores the delta from the first branch to the shared tail in a 16-bit field, which wraps above 65,535 branches and truncates the decision table. Reachability requires an application to compile an attacker-influenced alternation exceeding 65,535 fixed strings; affected decisions can admit denied input or reject allowed input.
The record
- CVE
- CVE-2026-13221
- Published
- Jul 13, 2026
- Updated
- Jul 13, 2026
- Vendor
- The Perl Foundation
- Product
- Perl
- Classifications
- CWE-190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 13, 2026CVE publishedPublication date reported by the CVE source.
- Jul 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <=5.43.9
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Large-trie regex reproducerproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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