{"id":"INC-anthropic-r1pqn1kb4hvk","kind":"incident","aliases":[],"related":[],"title":"Anthropic: Degraded functionality for Claude Cowork on Windows","description":"This issue has been resolved. Microsoft has released a September 14 Windows update that fixes it: https://support.microsoft.com/en-us/servicing/os/windows-11/2026/09/kb5129195-windows-11-24h2-25h2-security-update","summary":"Anthropic's status page reported degraded functionality for Claude Cowork on Windows, and the incident is marked resolved. The sources do not describe an attacker-usable flaw; the cause was a Windows-side issue fixed by Microsoft's September 14 update.","severity":"high","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[{"name":"Anthropic","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["ai","anthropic","claude-cowork","incident","llm","security","vendor","windows"],"not_affected_if":["non-windows-platforms"],"how_to_check":null,"fix":"Install the Microsoft Windows 11 September 14 security update (KB5129195 for 24H2/25H2) as linked in the incident; the incident itself is resolved.","status":"resolved","published_at":"2026-09-10T15:54:10+00:00","first_seen_at":"2026-10-23T19:12:22+00:00","triaged_at":"2026-10-23T21:50:52+00:00","updated_at":"2026-10-23T21:50:52+00:00","category":"vendor","confidence":0.5,"triage":{"at":"2026-10-23T21:50:52Z","model":"claude-haiku-5-5","output":{"fix":"Install the Microsoft Windows 11 September 14 security update (KB5129195 for 24H2/25H2) as linked in the incident; the incident itself is resolved.","reach":"unknown","impact":"low","summary":"Anthropic's status page reported degraded functionality for Claude Cowork on Windows, and the incident is marked resolved. The sources do not describe an attacker-usable flaw; the cause was a Windows-side issue fixed by Microsoft's September 14 update.","category":"vendor","who_cares":["claude-cowork","windows","anthropic"],"confidence":0.5,"needs_auth":"unknown","worst_case":"unknown","analyst_note":"Sources do not state whether this is a security flaw or only a service degradation; check the statuspage incident (https://stspg.io/5yp3rhhztm30) and the linked Microsoft KB for the actual cause.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["non-windows-platforms"],"user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.00047,"input_tokens":2781,"output_tokens":384,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'/en-us/servicing/os/windows-11/2026/09/kb5129195-windows-11-24h2-25h2-security-update':85C '14':65B,77C 'ai':14B 'anthrop':1A,15B,24B 'anthropic':11A,13A 'attack':49B 'attacker-us':48B 'caus':53B 'claud':5A,17B,32B 'claude-cowork':16B 'cowork':6A,18B,33B 'degrad':2A,29B 'describ':46B 'fix':60B,81C 'flaw':51B 'function':3A,30B 'inc':10A 'inc-anthropic-r1pqn1kb4hvk':9A 'incid':19B,38B 'issu':59B,68C 'llm':20B 'mark':40B 'microsoft':62B,72C 'page':27B 'r1pqn1kb4hvk':12A 'releas':74C 'report':28B 'resolv':41B,71C 'secur':21B 'septemb':64B,76C 'side':58B 'sourc':43B 'status':26B 'support.microsoft.com':84C 'support.microsoft.com/en-us/servicing/os/windows-11/2026/09/kb5129195-windows-11-24h2-25h2-security-update':83C 'updat':66B,79C 'usabl':50B 'vendor':22B 'window':8A,23B,35B,57B,78C 'windows-sid':56B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2026-09-10T15:54:10+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"statuspage","external_id":"anthropic:r1pqn1kb4hvk","url":"https://stspg.io/5yp3rhhztm30","severity":"high","published_at":"2026-09-10T15:54:10+00:00","modified_at":"2026-09-14T19:14:45+00:00","first_seen_at":"2026-10-23T19:12:22+00:00","fetched_at":"2026-10-25T18:56:17+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"}