{"id":"CVE-2026-117891","kind":"vulnerability","aliases":["CVE-2026-117891"],"related":[],"title":"Firefox: JavaScript JIT use-after-free could let a web page run code","description":"Use-after-free in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6.","summary":"A use-after-free bug in the JIT compiler of Firefox's JavaScript engine lets memory be reused after it is freed. Per the sources, it was fixed in Firefox 159 and Firefox ESR 115.44 and 153.6, and the sources do not say what an attacker gets beyond that memory-safety flaw.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["browsers","desktop","firefox","runtime"],"not_affected_if":[],"how_to_check":"- Run `firefox --version` (or check About Firefox) and compare against `159` for Firefox or `115.44` / `153.6` for the ESR branches\n- unknown for any other check, as the sources do not say which configurations are exposed","fix":"- Update Firefox to `159` or later\n- Update Firefox ESR to `115.44` or `153.6` or later","status":"open","published_at":"2026-10-27T14:16:44+00:00","first_seen_at":"2026-10-27T14:32:22+00:00","triaged_at":"2026-10-27T14:37:48+00:00","updated_at":"2026-10-27T14:37:48+00:00","category":"runtime","confidence":0.4,"triage":{"at":"2026-10-27T14:37:48Z","model":"claude-haiku-5-5","output":{"fix":"- Update Firefox to `159` or later\n- Update Firefox ESR to `115.44` or `153.6` or later","reach":"unknown","title":"Firefox: JavaScript JIT use-after-free could let a web page run code","impact":"high","summary":"A use-after-free bug in the JIT compiler of Firefox's JavaScript engine lets memory be reused after it is freed. Per the sources, it was fixed in Firefox 159 and Firefox ESR 115.44 and 153.6, and the sources do not say what an attacker gets beyond that memory-safety flaw.","category":"runtime","nicknames":[],"who_cares":["firefox","browsers","desktop"],"confidence":0.4,"needs_auth":"unknown","worst_case":"unknown; memory corruption in the JavaScript engine, impact not stated","analyst_note":"Check the Mozilla security advisory for this CVE for exploitation details, whether it is sandbox-escapable, and the exact affected version ranges, at https://nvd.nist.gov/vuln/detail/CVE-2026-117891.","how_to_check":"- Run `firefox --version` (or check About Firefox) and compare against `159` for Firefox or `115.44` / `153.6` for the ESR branches\n- unknown for any other check, as the sources do not say which configurations are exposed","needs_analyst":true,"not_affected_if":[],"who_is_affected":"Anyone running a Firefox build older than the fixed versions, including ESR installs, on desktops or managed fleets. The sources do not say whether a specific configuration or site is required, so unknown whether some setups can skip it.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000624,"input_tokens":3258,"output_tokens":597,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-117891':17A,20A '-2026':16A,19A '115.44':60B,98C '153.6':62B,102C '159':56B,95C 'attack':71B 'beyond':73B 'browser':21B 'bug':30B 'code':14A 'compil':34B 'compon':88C 'could':8A 'cve':15A,18A 'desktop':22B 'engin':39B,86C 'esr':59B,97C,101C 'firefox':1A,23B,36B,55B,58B,94C,96C,100C 'fix':53B,92C 'flaw':78B 'free':7A,29B,82C 'freed':47B 'get':72B 'javascript':2A,38B,85C 'jit':3A,33B,87C 'let':9A,40B 'memori':41B,76B 'memory-safeti':75B 'page':12A 'per':48B 'reus':43B 'run':13A 'runtim':24B 'safeti':77B 'say':68B 'sourc':50B,65B 'use':5A,27B,80C 'use-after-fre':4A,26B,79C 'vulner':90C 'web':11A","nicknames":[],"mitigations":[],"who_affected":"Anyone running a Firefox build older than the fixed versions, including ESR installs, on desktops or managed fleets. The sources do not say whether a specific configuration or site is required, so unknown whether some setups can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-27T14:16:44+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-117891","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-117891","severity":null,"published_at":"2026-10-27T14:16:44+00:00","modified_at":"2026-10-27T14:16:44+00:00","first_seen_at":"2026-10-27T14:32:22+00:00","fetched_at":"2026-10-27T14:32:22+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}