{"id":"CVE-2026-55087","summary":"Etherpad: x-proxy-path header reflected into admin HTML/JS/CSS (cache-poisoning XSS) and concatenated into redirect (open-redirect)","details":"Etherpad is a real-time collaborative editor. From 2.1.0 until 3.1.0, Etherpad uses the attacker-controlled x-proxy-path request header in src/node/hooks/express/admin.ts when substituting paths into HTML, JavaScript, and CSS under /admin without sanitization, Vary: x-proxy-path, or Cache-Control: private, no-store. A shared proxy or CDN can cache the resulting response and serve attacker-injected script to an administrator. In src/node/hooks/express/specialpages.ts, version 3.0.0 also accepts a protocol-relative x-proxy-path value when constructing the /p/:pad/timeslider redirect, allowing redirection to an attacker-controlled host. The issues are exploitable when the deployment permits client-supplied x-proxy-path headers to reach Etherpad. This issue is fixed in version 3.1.0.","aliases":["GHSA-fjgc-3mj7-8rg8"],"modified":"2026-08-23T03:42:43.557534767Z","published":"2026-08-19T19:29:16.221Z","database_specific":{"cna_assigner":"GitHub_M","cwe_ids":["CWE-444","CWE-601","CWE-79"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55087.json"},"references":[{"type":"WEB","url":"https://github.com/ether/etherpad/tree/3.1.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55087.json"},{"type":"ADVISORY","url":"https://github.com/ether/etherpad/security/advisories/GHSA-fjgc-3mj7-8rg8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55087"},{"type":"FIX","url":"https://github.com/ether/etherpad/commit/8c6104c5d5daf41f0d454acc04d42dffa0e0d996"},{"type":"FIX","url":"https://github.com/ether/etherpad/pull/7784"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ether/etherpad","events":[{"introduced":"c45b7a361e56e6c753cd1c9b8cc4e1017090ce9c"},{"fixed":"8c6104c5d5daf41f0d454acc04d42dffa0e0d996"}],"database_specific":{"source":["AFFECTED_FIELD","REFERENCES"],"extracted_events":[{"introduced":"2.1.0"},{"fixed":"3.1.0"}]}}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55087.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"}]}