{"cve":"CVE-2026-19487","nvd":{"published":"2026-08-13T16:17:59.440","modified":"2026-08-28T15:42:20.060","status":"Awaiting Analysis","description":"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.\n\nThe 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.\n\nExample:\n\n  \"ABCDE\" =~ m/ABCF|BCDE|C/;    # matches C at offset 2, not BCDE\n  \"ABCDE\" =~ m/ABCF|BCDE|C(G)/; # no match, BCDE missed\n\nAn 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_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","score":5.3},"cwes":["CWE-670"],"references":["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"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:48:17.459049833+00:00"},"epss":{"cve":"CVE-2026-19487","score":0.00418,"percentile":0.36174,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}