Perl up to 5.41.8 Aho-Corasick Prescan S_find_byclass input validation

Summaryinfo

A vulnerability has been found in Perl up to 5.41.8 and classified as critical. This impacts the function S_find_byclass of the component Aho-Corasick Prescan. The manipulation leads to input validation. This vulnerability is documented as CVE-2026-19487. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in Perl up to 5.41.8 and classified as critical. This issue affects the function S_find_byclass of the component Aho-Corasick Prescan. The manipulation with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-19487 since 08/10/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 5.41.9 eliminates this vulnerability.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

• Programming Language Software

Name

• Perl

Version

• 5.41.0
• 5.41.1
• 5.41.2
• 5.41.3
• 5.41.4
• 5.41.5
• 5.41.6
• 5.41.7
• 5.41.8

License

• open-source

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Discussion