CVE-2026-55087
MediumCVSS 6.1Exploitation Probability (EPSS)
Low risk45th percentile - higher than 45% of all known CVEs
Summary
Etherpad versions 2.1.0 to 3.1.0 use the attacker-controlled x-proxy-path header when substituting paths into HTML, JavaScript, and CSS under /admin without sanitization, Vary, or Cache-Control. A shared proxy or CDN can cache the response and serve attacker-injected script to an administrator. Version 3.0.0 also accepts a protocol-relative x-proxy-path value, allowing redirection to an attacker-controlled host.
Risk Assessment
The risk includes XSS attacks on administrators, session hijacking, and redirects to malicious sites. The vulnerability is exploitable when the header can be controlled by the client.
Recommendation
Upgrade Etherpad to version 3.1.0 or later. Also, configure the server to ignore or sanitize the x-proxy-path header from clients.
Original NVD description (English source)
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.