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

Quick assessment

Affected
ether etherpad
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

etherpad是ETHER组织的一个支持多人实时在线协作的文档编辑工具。 ETHER etherpad 2.1.0版本至3.1.0之前版本存在安全漏洞，该漏洞源于对x-proxy-path请求头处理不当，可能导致跨站脚本攻击或重定向到攻击者控制的地址。

CVSS 6.1 · Medium EPSS 0.57% · P45

Public Exploits 1

Nuclei · 1 CVE-2026-55087.yaml [template]

Affected Version Matrix 1

VendorProduct Version RangeStatus
ether etherpad >= 2.1.0, < 3.1.0 affected
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I. Basic Information for CVE-2026-55087

Vulnerability Information
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Vulnerability Title
Etherpad: x-proxy-path header reflected into admin HTML/JS/CSS (cache-poisoning XSS) and concatenated into redirect (open-redirect)
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
ETHER etherpad 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
etherpad是ETHER组织的一个支持多人实时在线协作的文档编辑工具。 ETHER etherpad 2.1.0版本至3.1.0之前版本存在安全漏洞，该漏洞源于对x-proxy-path请求头处理不当，可能导致跨站脚本攻击或重定向到攻击者控制的地址。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ether etherpad >= 2.1.0, < 3.1.0 -

II. Public POCs for CVE-2026-55087

# POC Description Source Link Shenlong Link
1 Etherpad versions 2.1.0 through 3.0.0 reflect the x-proxy-path request header into admin HTML, JavaScript, and CSS responses without sanitization. An attacker can abuse this behavior to inject crafted content into generated resource URLs, enabling cross-site scripting and cache poisoning scenarios. https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-55087.yaml POC Details
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III. Intelligence Information for CVE-2026-55087

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Patches & Fixes for CVE-2026-55087 (1)

Vendor Advisories for CVE-2026-55087 (1)

Same Patch Batch · ether · 2026-08-19 · 6 CVEs total

CVE-2026-55089 9.9 CRITICAL Etherpad: JWT `admin` claim presence-only check lets non-admin OAuth users invoke every Et
CVE-2026-55085 9.6 CRITICAL Etherpad: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripti
CVE-2026-55088 6.8 MEDIUM Etherpad: Device-to-device author-token transfer endpoint is replayable, never expires, an
CVE-2026-55090 5.3 MEDIUM Etherpad: Stored XSS in HTML export via unescaped attribute-pool values
CVE-2026-55086 4.2 MEDIUM Etherpad: Import/export use Math.random() for temp file paths; predictable paths on shared

IV. Related Vulnerabilities

Same product: etherpad
Same vendor: ether
Same weakness: CWE-79

V. Comments for CVE-2026-55087

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