{"id":"CVE-2026-117920","kind":"vulnerability","aliases":["CVE-2026-117920"],"related":[],"title":"Firefox: use-after-free in HTML parser can crash or run code","description":"Use-after-free in the DOM: HTML Parser component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.","summary":"A use-after-free bug in the DOM HTML Parser component of Firefox was fixed in Firefox 159 and Firefox ESR 153.6. Freed memory being reused can crash the browser or, in the worst case, let a crafted web page run code.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["browsers","desktop","firefox","runtime"],"not_affected_if":["up-to-date-firefox"],"how_to_check":"- Check the installed Firefox version (Help > About Firefox) or run `firefox --version`\n- unknown for other checks, the sources do not say","fix":"- Update Firefox to `159` or later\n- Update Firefox ESR to `153.6` or later","status":"open","published_at":"2026-10-27T14:16:47+00:00","first_seen_at":"2026-10-27T14:32:22+00:00","triaged_at":"2026-10-27T14:37:19+00:00","updated_at":"2026-10-27T14:37:19+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-27T14:37:19Z","model":"claude-haiku-5-5","output":{"fix":"- Update Firefox to `159` or later\n- Update Firefox ESR to `153.6` or later","reach":"internet","title":"Firefox: use-after-free in HTML parser can crash or run code","impact":"high","summary":"A use-after-free bug in the DOM HTML Parser component of Firefox was fixed in Firefox 159 and Firefox ESR 153.6. Freed memory being reused can crash the browser or, in the worst case, let a crafted web page run code.","category":"runtime","nicknames":[],"who_cares":["firefox","desktop","browsers"],"confidence":0.5,"needs_auth":"no","worst_case":"Browser crash, or code runs when a victim visits a crafted page","analyst_note":"Check Mozilla's Firefox 159 and ESR 153.6 release notes or the Mozilla security advisory for the CVE to confirm severity and exploitation details.","how_to_check":"- Check the installed Firefox version (Help > About Firefox) or run `firefox --version`\n- unknown for other checks, the sources do not say","needs_analyst":true,"not_affected_if":["up-to-date-firefox"],"who_is_affected":"Anyone running Firefox or Firefox ESR older than the fixed versions, including browsers on managed desktops. The sources do not say which configurations are affected beyond the version. Servers and applications that do not run a Firefox browser can skip it.","user_interaction":"yes","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000585,"input_tokens":3242,"output_tokens":522,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-117920':16A,19A '-2026':15A,18A '153.6':46B,87C '159':42B,83C 'browser':20B,54B 'bug':29B 'case':59B 'code':13A,66B 'compon':35B,76C 'craft':62B 'crash':10A,52B 'cve':14A,17A 'desktop':21B 'dom':32B,73C 'esr':45B,86C 'firefox':1A,22B,37B,41B,44B,82C,85C 'fix':39B,80C 'free':5A,28B,70C 'freed':47B 'html':7A,33B,74C 'let':60B 'memori':48B 'page':64B 'parser':8A,34B,75C 'reus':50B 'run':12A,65B 'runtim':23B 'use':3A,26B,68C 'use-after-fre':2A,25B,67C 'vulner':78C 'web':63B 'worst':58B","nicknames":[],"mitigations":[],"who_affected":"Anyone running Firefox or Firefox ESR older than the fixed versions, including browsers on managed desktops. The sources do not say which configurations are affected beyond the version. Servers and applications that do not run a Firefox browser can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-27T14:16:47+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-117920","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-117920","severity":null,"published_at":"2026-10-27T14:16:47+00:00","modified_at":"2026-10-27T14:16:47+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"}