{"schemaVersion":3,"id":"CVE-2026-19487","aliases":["UBUNTU-CVE-2026-19487","DEBIAN-CVE-2026-19487"],"status":"published","duplicateOf":null,"title":null,"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.","dates":{"published":"2026-08-13T15:51:04.090Z","modified":"2026-08-13T20:12:11.045Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":5.3,"severity":"medium","version":"3.1","versionLabel":"v3.1","source":"CVE.org","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","computed":false,"selection":"backend-summary"},"metrics":[{"version":"3.1","versionLabel":"v3.1","source":"CVE.org","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","exploitability":null,"impact":null,"computed":false},{"version":"3.1","versionLabel":"v3.1","source":"OSV · Ubuntu","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","exploitability":10,"impact":2.3,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"OSV · Debian","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","exploitability":10,"impact":2.3,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":5.3,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.00418,"percentile":0.35016,"severity":"low","asOf":"2026-10-21T00:00:00.000Z","change":{"pp":0,"baselineDate":"2026-09-21T00:00:00.000Z","baselineScore":0.00418},"history":[{"date":"2026-09-14T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-15T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-16T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-17T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-18T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-19T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-20T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-21T00:00:00.000Z","score":0.00418,"percentile":0.35016}],"last30":[{"date":"2026-09-21T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00418,"percentile":null},{"date":"2026-10-21T00:00:00.000Z","score":0.00418,"percentile":0.35016}]},"kev":{"state":"not-listed","entries":[],"listedCount":0,"totalCatalogs":3,"catalogs":[{"source":"cisa","label":"CISA","listed":false,"entry":null},{"source":"enisa","label":"ENISA","listed":false,"entry":null},{"source":"circl","label":"CIRCL","listed":false,"entry":null}]},"ransomware":{"state":"none-recorded","sources":[]},"exploits":[],"exploitCount":0,"weaknesses":[{"id":"CWE-670","name":"Always-Incorrect Control Flow Implementation","description":"The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.","type":"weakness","status":"Draft","abstraction":"Class","likelihoodOfExploit":null,"url":"https://cwe.mitre.org/data/definitions/670.html"}],"affected":[{"vendor":"debian","product":"perl","name":"perl","label":"perl","ecosystem":"Debian","cpePart":null,"purl":"pkg:deb/debian/perl","purlType":"deb","versions":[{"text":"< 5.36.0-7+deb12u4","noFixRecorded":false,"fixedIn":null},{"text":"< 5.40.1-6+deb13u1","noFixRecorded":false,"fixedIn":null},{"text":"< 5.42.2-3","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 5.36.0-7+deb12u4 | < 5.40.1-6+deb13u1 | < 5.42.2-3","eol":null,"hubHref":null},{"vendor":"ubuntu","product":"perl","name":"perl","label":"perl","ecosystem":"Ubuntu","cpePart":null,"purl":"pkg:deb/ubuntu/perl","purlType":"deb","versions":[{"text":"< 5.18.2-2ubuntu1.7+esm9","noFixRecorded":false,"fixedIn":null},{"text":"< 5.22.1-9ubuntu0.9+esm4","noFixRecorded":false,"fixedIn":null},{"text":"< 5.26.1-6ubuntu0.7+esm4","noFixRecorded":false,"fixedIn":null},{"text":"< 5.30.0-9ubuntu0.5+esm4","noFixRecorded":false,"fixedIn":null},{"text":"< 5.34.0-3ubuntu1.9","noFixRecorded":false,"fixedIn":null},{"text":"< 5.38.2-3.2ubuntu0.6","noFixRecorded":false,"fixedIn":null},{"text":"< 5.40.1-7ubuntu0.2","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 5.18.2-2ubuntu1.7+esm9 | < 5.22.1-9ubuntu0.9+esm4 | < 5.26.1-6ubuntu0.7+esm4 | < 5.30.0-9ubuntu0.5+esm4 | < 5.34.0-3ubuntu1.9 | < 5.38.2-3.2ubuntu0.6 | < 5.40.1-7ubuntu0.2","eol":null,"hubHref":null}],"affectedCount":2,"eol":{"hasEol":false,"count":0},"references":[{"url":"https://github.com/Perl/perl5/commit/1a21abacaf6f684928bae8baaa153733c8c238eb.patch","label":"github.com/Perl/perl5/commit/1a21abacaf6f684928bae8baaa153733c8c238eb.patch","hostname":"github.com","tags":["Patch"]},{"url":"https://github.com/Perl/perl5/issues/22892","label":"github.com/Perl/perl5/issues/22892","hostname":"github.com","tags":["Issue Tracking","REPORT"]},{"url":"http://www.openwall.com/lists/oss-security/2026/08/13/8","label":"www.openwall.com/lists/oss-security/2026/08/13/8","hostname":"www.openwall.com","tags":[]},{"url":"https://ubuntu.com/security/CVE-2026-19487","label":"ubuntu.com/security/CVE-2026-19487","hostname":"ubuntu.com","tags":["REPORT"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-19487","label":"www.cve.org/CVERecord?id=CVE-2026-19487","hostname":"www.cve.org","tags":["REPORT"]},{"url":"https://lists.security.metacpan.org/cve-announce/msg/42658992/","label":"lists.security.metacpan.org/cve-announce/msg/42658992/","hostname":"lists.security.metacpan.org","tags":["REPORT"]},{"url":"https://ubuntu.com/security/notices/USN-8736-1","label":"ubuntu.com/security/notices/USN-8736-1","hostname":"ubuntu.com","tags":["Advisory"]},{"url":"https://ubuntu.com/security/notices/USN-8736-2","label":"ubuntu.com/security/notices/USN-8736-2","hostname":"ubuntu.com","tags":["Advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-19487","label":"security-tracker.debian.org/tracker/CVE-2026-19487","hostname":"security-tracker.debian.org","tags":["Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-19487","label":"nvd.nist.gov/vuln/detail/CVE-2026-19487","hostname":"nvd.nist.gov","tags":["Oval","Advisory"]}],"lineage":{"upstream":[],"downstream":["USN-8736-1","USN-8736-2"],"duplicates":[],"related":["USN-8736-1","USN-8736-2"]},"timeline":[{"kind":"published","date":"2026-08-13T15:51:04.090Z","label":"Published","detail":"Vulnerability first disclosed.","source":null},{"kind":"modified","date":"2026-08-13T20:12:11.045Z","label":"Last modified","detail":"Vulnerability information updated.","source":null}],"risk":{"score":21,"level":"low","profile":"Default","thresholds":{"critical":75,"high":50,"medium":25,"low":10}},"meta":{"dataAsOf":"2026-10-22T09:02:28.831Z","stale":false,"partial":false}}