{"id":"GHSA-j944-w549-3453","summary":"Cinny vulnerable to access token disclosure via invalidated emoji pack avatar URL in service worker","details":"### 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","aliases":["CVE-2026-42553"],"modified":"2026-06-09T00:00:19.393740437Z","published":"2026-05-07T16:40:52Z","database_specific":{"cwe_ids":["CWE-20"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-05-07T16:40:52Z","nvd_published_at":"2026-05-27T18:16:22Z"},"references":[{"type":"WEB","url":"https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42553"},{"type":"PACKAGE","url":"https://github.com/cinnyapp/cinny"},{"type":"WEB","url":"https://github.com/cinnyapp/cinny/releases/tag/v4.10.3"}],"affected":[{"package":{"name":"cinny","ecosystem":"npm","purl":"pkg:npm/cinny"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"4.10.3"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-j944-w549-3453/GHSA-j944-w549-3453.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}