{"id":"CVE-2026-109721","title":"Incorrect boundary conditions in the JavaScript Engine: JIT component","summary":"Incorrect boundary conditions in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.","severity":"medium","published":"2026-10-13","updated":"2026-10-13","sourceUpdated":"2026-10-13T19:18:35.833","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-109721","references":[{"url":"https://bugzilla.mozilla.org/show_bug.cgi?id=2074161","label":"security@mozilla.org"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-106/","label":"security@mozilla.org"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-108/","label":"security@mozilla.org"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-109/","label":"security@mozilla.org"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-110/","label":"security@mozilla.org"}],"tags":["nvd","cve.org","exploit-available"],"ingestedAt":"2026-10-13T13:27:03.996Z","vendor":"Mozilla","product":"Firefox","affected":["Firefox","Thunderbird"],"epss":0.00278,"epssPercentile":0.20122,"exploits":{"github":1,"githubRepos":["https://github.com/Scyrix-LLC/CVE-2026-109721"],"checkedAt":"2026-10-27T16:56:19.038Z"},"exploitAvailable":true,"cvss":5.4,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N","ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-10-19T11:07:02.716884Z"},"cvssSource":"adp","slug":"CVE-2026-109721","body":"## Overview\n\nIncorrect boundary conditions in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":42,"depthScoreParts":{"impact":29.7,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[{"seq":224913,"id":"CVE-2026-109721","ts":1792412889042,"field":"cvss","old":null,"new":"5.4"},{"seq":224912,"id":"CVE-2026-109721","ts":1792412889042,"field":"severity","old":"none","new":"medium"},{"seq":223895,"id":"CVE-2026-109721","ts":1792268378539,"field":"exploit_available","old":"false","new":"true"}]}