ether Etherpad up to 3.0.x Proxy Header admin.ts x-proxy-path redirect

Summaryinfo

A vulnerability described as problematic has been identified in ether Etherpad up to 3.0.x. Affected by this issue is some unknown functionality of the file src/node/hooks/express/admin.ts of the component Proxy Header Handler. Executing a manipulation of the argument x-proxy-path can lead to redirect. This vulnerability appears as CVE-2026-55087. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability classified as problematic was found in ether Etherpad up to 3.0.x. This vulnerability affects an unknown code block of the file src/node/hooks/express/admin.ts of the component Proxy Header Handler. The manipulation of the argument x-proxy-path with an unknown input leads to a redirect vulnerability. The CWE definition for the vulnerability is CWE-601. A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks. As an impact it is known to affect integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-55087 since 06/16/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1204.001.

Upgrading to version 3.1.0 eliminates this vulnerability.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Vendor

• ether

Name

• Etherpad

Version

• 3.0

Website

• Product: https://github.com/ether/etherpad/

CPE 2.3info

• 🔒

CPE 2.2info

• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Discussion