{"cve":"CVE-2026-56812","nvd":{"published":"2026-07-07T16:16:40.920","modified":"2026-10-25T20:10:00.147","status":"Modified","description":"Improper Check for Unusual or Exceptional Conditions vulnerability in phoenixframework phoenix (Presence JavaScript client) allows an attacker with ordinary channel access to cause a persistent client-side denial of service against every viewer of a presence channel topic.\n\nThis vulnerability is associated with program files assets/js/phoenix/presence.js and program routines Presence.syncState and Presence.syncDiff.\n\nThe Phoenix JavaScript presence client checks whether a presence already exists with a bare truthiness test (state[key]) instead of an own-property check. Presence keys can be attacker-controlled, because applications track presences under a username or id supplied by the client. A user who joins a channel choosing a key that is an Object.prototype member name (__proto__, constructor, toString, hasOwnProperty, and similar) makes that lookup return JavaScript's built-in Object.prototype instead of undefined. Because the prototype is truthy, the code treats it as an existing presence and reads .metas.map(...) off it, which throws an uncaught TypeError.\n\nThe exception propagates out of the presence message handler, so the local state is never updated and onSync() never fires. Because the malicious key is tracked on the server, it is re-pushed on every presence update and keeps re-throwing, so presence sync stays broken for every viewer of that channel topic until the attacker leaves. Both syncState and syncDiff use the same unsafe existence-check pattern. The impact is limited to the affected topic and is a read-time confusion of the prototype object, not a mutation of Object.prototype (it is not prototype pollution).\n\nThis issue affects phoenix: from 1.2.0-rc.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9; phoenix: from 1.2.0-rc.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","score":6.3},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-754"],"references":["https://cna.erlef.org/cves/CVE-2026-56812.html","https://github.com/phoenixframework/phoenix/commit/2270aaf21bd02c6a6a1022820564efb605a97655","https://github.com/phoenixframework/phoenix/commit/7f7b971c1ea0994e3fbd1c11ddb05e780bd38ad8","https://github.com/phoenixframework/phoenix/commit/89a1c4be161e436241e12b2378a719904b9bd96f","https://github.com/phoenixframework/phoenix/commit/b90b22521465ece00eb5a19d5aa2b9465b209c85"],"products":["phoenixframework:phoenix"],"source":"nvd","synced_at":"2026-10-25T23:44:34.550481224+00:00"},"epss":{"cve":"CVE-2026-56812","score":0.00796,"percentile":0.56191,"date":"2026-10-25"},"kev":null,"osv":[{"id":"EEF-CVE-2026-56812","url":"https://osv.dev/vulnerability/EEF-CVE-2026-56812","summary":"Phoenix JavaScript presence client crashes on presence keys colliding with Object.prototype members in Presence.syncState/syncDiff","modified":"2026-09-24T21:30:06.586470584Z","packages":[{"ecosystem":"Hex","name":"phoenix","purl":"pkg:hex/phoenix","ranges":[">=1.2.0-rc.0 <1.5.15",">=1.6.0-rc.0 <1.6.17",">=1.7.0-rc.0 <1.7.24",">=1.8.0-rc.0 <1.8.9"],"fixed":["1.5.15","1.6.17","1.7.24","1.8.9"]},{"ecosystem":"npm","name":"phoenix","purl":"pkg:npm/phoenix","ranges":[">=1.2.0-rc.0 <1.5.15",">=1.6.0-rc.0 <1.6.17",">=1.7.0-rc.0 <1.7.24",">=1.8.0-rc.0 <1.8.9"],"fixed":["1.5.15","1.6.17","1.7.24","1.8.9"]},{"ecosystem":null,"name":null,"purl":null,"ranges":["v1.5.13, v1.6.16, v1.7.23, v1.8.8, v1.8.7 and 80 more"],"fixed":[]}]},{"id":"GHSA-63mc-hw7g-86rr","url":"https://osv.dev/vulnerability/GHSA-63mc-hw7g-86rr","summary":"Phoenix: Presence keys colliding with `Object.prototype` members break existence checks","modified":"2026-09-03T20:45:04.985092212Z","packages":[{"ecosystem":"Hex","name":"phoenix","purl":"pkg:hex/phoenix","ranges":[">=1.2.0-rc.0 <1.5.15"],"fixed":["1.5.15"]},{"ecosystem":"Hex","name":"phoenix","purl":"pkg:hex/phoenix","ranges":[">=1.6.0-rc.0 <1.6.17"],"fixed":["1.6.17"]},{"ecosystem":"Hex","name":"phoenix","purl":"pkg:hex/phoenix","ranges":[">=1.7.0-rc.0 <1.7.24"],"fixed":["1.7.24"]},{"ecosystem":"Hex","name":"phoenix","purl":"pkg:hex/phoenix","ranges":[">=1.8.0-rc.0 <1.8.9"],"fixed":["1.8.9"]},{"ecosystem":"npm","name":"phoenix","purl":"pkg:npm/phoenix","ranges":[">=1.2.0-rc.0 <1.5.15"],"fixed":["1.5.15"]},{"ecosystem":"npm","name":"phoenix","purl":"pkg:npm/phoenix","ranges":[">=1.6.0-rc.0 <1.6.17"],"fixed":["1.6.17"]},{"ecosystem":"npm","name":"phoenix","purl":"pkg:npm/phoenix","ranges":[">=1.7.0-rc.0 <1.7.24"],"fixed":["1.7.24"]},{"ecosystem":"npm","name":"phoenix","purl":"pkg:npm/phoenix","ranges":[">=1.8.0-rc.0 <1.8.9"],"fixed":["1.8.9"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}