{"id":"GHSA-j944-w549-3453","revision":"f065706511424a418df91db7cbd86442","records":[{"revision":"f065706511424a418df91db7cbd86442","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-j944-w549-3453","aliases":["CVE-2026-42553"],"title":"Cinny vulnerable to access token disclosure via invalidated emoji pack avatar URL in service worker","description":"### Impact\nA remote authenticated attacker who shares a room with a victim and has permissions to create room emotes (for example in a DM) can cause the victim's client to send their Matrix access token to an attacker-controlled server. This occurs when the victim opens the emoji or sticker picker for the room containing a malicious emote pack. \n\nThe root causes are: \n\n(1) an incorrect fallback in EmojiBoard that uses untrusted `pack.meta.avatar` (user-controlled) without converting/validating it as an MXC URL, allowing arbitrary HTTP(S) URLs to be used; and \n\n(2) the service worker attaching the user's Authorization bearer token to all outbound GET requests whose URL contains `/_matrix/client/v1/media/download` or `/_matrix/client/v1/media/thumbnail` without verifying the request host matches the configured homeserver origin. An attacker-controlled URL containing those path fragments and permissive CORS will receive the victim's Authorization header (access token). \n\nImpacted users: anybody using affected Cinny web app versions who opens the emoji/sticker picker in a room containing a malicious emote pack and who is logged in (authenticated).\n\n### Patches\nVersion with fixes: https://github.com/cinnyapp/cinny/releases/tag/v4.10.3","state":0,"publishedAt":"2026-05-07T16:40:52+00:00","modifiedAt":"2026-06-09T00:00:19.3937404+00:00","affected":[{"ecosystem":"npm","name":"cinny","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"4.10.3"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V4","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"HIGH"}],"references":["https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453","https://nvd.nist.gov/vuln/detail/CVE-2026-42553","https://github.com/cinnyapp/cinny","https://github.com/cinnyapp/cinny/releases/tag/v4.10.3"],"sourceUrl":"https://github.com/advisories/GHSA-j944-w549-3453","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-j944-w549-3453","identifiers":["GHSA-j944-w549-3453","CVE-2026-42553"]},"retained":false,"historicalAffected":[]}],"coverage":[]}