Etherpad: x-proxy-path header reflected into admin HTML/JS/CSS (cache-poisoning XSS) and concatenated into redirect (open-redirect)

published 2026-08-13 2 mo ago modified 2026-09-09 1 mo ago also GHSA-fjgc-3mj7-8rg8 , EUVD-2026-62721

cvss: 6.1; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 47%
public exploits: 0; none known, plus a Nuclei check

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.

Patch / fix

fixed in 1 links 6

npm ep_etherpad-lite 3.1.0

github.com/ether/etherpad@8c6104c commit
github.com/ether/etherpad@451bd9c commit
github.com/ether/etherpad@63e9b2d commit
github.com/ether/etherpad#7784 pull request
github.com/ether/etherpad#6399 pull request
github.com/ether/etherpad#7710 pull request

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2 mo ago (2026-08-21)

Exploit prediction

0.58% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

Nuclei template Etherpad 2.1.0 <= 3.0.0 - Cross-Site Scripting nuclei detection template

CVSS scores

assigned by	version	score	vector
CNA	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	ep_etherpad-lite	>=2.1.0, <3.1.0	3.1.0

Affected products

ether etherpad

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation
CWE-444 Inconsistent Interpretation of HTTP Requests
CWE-601 URL Redirection to Untrusted Site

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary