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CVE-2026-55087 medium CVSS 6.1

Cross-Site Scripting (XSS) in ep_etherpad-lite (CVE-2026-55087)

Summary

Cross-site scripting in ep_etherpad-lite (CVE-2026-55087). Risk of unauthorized operations or information disclosure. Exploitable via String.prototype.replaceAll. Mitigation: upgrade to 3.1.0 or later.

Original description

The description as published by the source.

GHSA-03 — x-proxy-path header reflected into admin HTML/JS/CSS (cache-poisoning XSS) and concatenated into redirect (open-redirect)

Severity: Medium
CVSS v3.1 vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS suggested base score: ~6.1 — Medium
(Re-validate in the first.gov calculator before filing. Score depends heavily on whether you assume a cooperative cache exists in front of the deployment — single-origin admin-only ops with no shared cache push toward 4.x; cache-poisoning against a CDN pushes toward 7.x.)
CWE: CWE-79 Improper Neutralization of Input During Web Page Generation, CWE-601 URL Redirection to Untrusted Site, CWE-444 Inconsistent Interpretation of HTTP Requests

Title

x-proxy-path request header is interpolated into admin HTML/JS/CSS without sanitisation (cache-poisoning XSS) and into a /p/:pad/timeslider redirect target (open-redirect via protocol-relative URL)

Description

Etherpad lets operators run behind a reverse proxy that prefixes every route with a subpath (e.g. /pad/etherpad/...). The proxy is expected to set x-proxy-path: /pad/etherpad on every request so that server-rendered links, asset URLs, and redirects know to include the prefix. Two server-side call sites historically processed this header:

Issue 3a — src/node/hooks/express/admin.ts (XSS, cache-poisoning)

The admin static-serving handler read req.header('x-proxy-path') and substituted it into the response body of every .html/`.js…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-55087 has been found in ep_etherpad-lite.
Attackers can target a specific entry point like String.prototype.replaceAll over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: upgrade ep_etherpad-lite to 3.1.0 or later.
If unsure, ask your IT team or search "ep_etherpad-lite CVE-2026-55087" on the vendor's site.

CVE-2026-55087 (ep_etherpad-lite) — CWE-79 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: String.prototype.replaceAll / Vary / sanitizeProxyPath / Location
Patched: 3.1.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in ep_etherpad-lite. Attackers reach the vulnerable code path via String.prototype.replaceAll without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of ep_etherpad-lite. Attack surface: String.prototype.replaceAll / Vary / sanitizeProxyPath / Location.

🔥 Severity

Severity: Medium (CVSS 6.1/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 3.1.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'ep_etherpad-lite' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'ep_etherpad-lite' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で ep_etherpad-lite を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade ep_etherpad-lite to 3.1.0

    ステージング環境で 3.1.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm ep_etherpad-lite
[{"type":"SEMVER","events":[{"introduced":"2.1.0"},{"fixed":"3.1.0"}]}]

References

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