{"id":"CVE-2026-123309","kind":"vulnerability","aliases":["CVE-2026-123309"],"related":[],"title":"IntelliJ IDEA: stored XSS via Markdown preview on built-in web server","description":"In JetBrains IntelliJ IDEA before 2026.3, \n2026.2.4 stored XSS was possible on the built-in web server via Markdown preview","summary":"In JetBrains IntelliJ IDEA before 2026.3 and 2026.2.4, a Markdown preview served by the built-in web server could store malicious script. A script running in the browser of a developer who views that preview could act with that developer's access.","severity":"medium","cvss":6.1,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["intellij-idea","jetbrains","markdown","package","xss"],"not_affected_if":["updated-ide-version"],"how_to_check":"- Check the IntelliJ IDEA version under Help > About and compare it with `2026.3` and `2026.2.4`\n- Confirm whether the built-in web server is in use for Markdown preview in your IDE setup","fix":"- IntelliJ IDEA: move to `2026.3` or `2026.2.4`, per the sources' affected range","status":"open","published_at":"2026-11-06T11:17:10+00:00","first_seen_at":"2026-11-06T11:41:25+00:00","triaged_at":"2026-11-06T11:42:23+00:00","updated_at":"2026-11-06T11:42:23+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-11-06T11:42:23Z","model":"claude-haiku-5-5","output":{"fix":"- IntelliJ IDEA: move to `2026.3` or `2026.2.4`, per the sources' affected range","reach":"unknown","title":"IntelliJ IDEA: stored XSS via Markdown preview on built-in web server","impact":"medium","summary":"In JetBrains IntelliJ IDEA before 2026.3 and 2026.2.4, a Markdown preview served by the built-in web server could store malicious script. A script running in the browser of a developer who views that preview could act with that developer's access.","audience":"developers","category":"package","nicknames":[],"who_cares":["intellij-idea","jetbrains","markdown","xss"],"confidence":0.6,"fix_status":"available","needs_auth":"unknown","worst_case":"Script runs in a developer's browser via stored content","analyst_note":"Check the JetBrains security bulletin to confirm the fixed versions and whether exploitation requires a crafted Markdown file or a network path.","how_to_check":"- Check the IntelliJ IDEA version under Help > About and compare it with `2026.3` and `2026.2.4`\n- Confirm whether the built-in web server is in use for Markdown preview in your IDE setup","plain_action":"","needs_analyst":true,"not_affected_if":["updated-ide-version"],"who_is_affected":"Developers running IntelliJ IDEA versions before 2026.3 or 2026.2.4 who use the built-in web server with Markdown preview. The sources do not describe any server-side exposure beyond the IDE itself, so teams that only use updated IDE builds can skip it.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"medium"},"cost_usd":0.00071,"input_tokens":4194,"output_tokens":582,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-123309':16A,19A '-2026':15A,18A '2026.2.4':34B,76C '2026.3':32B,75C 'access':69B 'act':64B 'browser':55B 'built':10A,42B,84C 'built-in':9A,41B,83C 'could':46B,63B 'cve':14A,17A 'develop':58B,67B 'idea':2A,22B,30B,73C 'intellij':1A,21B,29B,72C 'intellij-idea':20B 'jetbrain':23B,28B,71C 'malici':48B 'markdown':6A,24B,36B,89C 'packag':25B 'possibl':80C 'preview':7A,37B,62B,90C 'run':52B 'script':49B,51B 'serv':38B 'server':13A,45B,87C 'store':3A,47B,77C 'via':5A,88C 'view':60B 'web':12A,44B,86C 'xss':4A,26B,78C","nicknames":[],"mitigations":[],"who_affected":"Developers running IntelliJ IDEA versions before 2026.3 or 2026.2.4 who use the built-in web server with Markdown preview. The sources do not describe any server-side exposure beyond the IDE itself, so teams that only use updated IDE builds can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"developers","plain_action":null,"pkeys":[],"ptokens":[],"labels":["intellijidea","jetbrains","markdown","medium","package","xss"],"campaign_type":null,"search_a":"'-123309':16A,19A '-2026':15A,18A 'built':10A 'built-in':9A 'cve':14A,17A 'idea':2A 'intellij':1A 'markdown':6A 'preview':7A 'server':13A 'store':3A 'via':5A 'web':12A 'xss':4A","search_b":"'2026.2.4':34B '2026.3':32B 'access':69B 'act':64B 'browser':55B 'built':42B 'built-in':41B 'could':46B,63B 'develop':58B,67B 'idea':22B,30B 'intellij':21B,29B 'intellij-idea':20B 'jetbrain':23B,28B 'malici':48B 'markdown':24B,36B 'packag':25B 'preview':37B,62B 'run':52B 'script':49B,51B 'serv':38B 'server':45B 'store':47B 'view':60B 'web':44B 'xss':26B","search_c":"'2026.2.4':76C '2026.3':75C 'built':84C 'built-in':83C 'idea':73C 'intellij':72C 'jetbrain':71C 'markdown':89C 'possibl':80C 'preview':90C 'server':87C 'store':77C 'via':88C 'web':86C 'xss':78C","first_public_at":"2026-11-06T11:17:10+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","cvss_by":"cve@jetbrains.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-123309","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-123309","severity":null,"published_at":"2026-11-06T11:17:10+00:00","modified_at":"2026-11-06T11:17:10+00:00","first_seen_at":"2026-11-06T11:41:25+00:00","fetched_at":"2026-11-06T11:41:25+00:00","note":null}],"documents":[],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}