CVE-2026-55087Public exploitNetwork attack vector

Admin script execution via x-proxy-path cache poisoning

Published Aug 19, 2026 · Updated Aug 19, 2026

Cross-site scripting in Etherpad before 3.1.0 allows remote attackers to run script in an administrator's browser via x-proxy-path. In src/node/hooks/express/admin.ts, Etherpad substitutes req.header('x-proxy-path') into /admin HTML, JavaScript, and CSS with replaceAll and no response variance controls; version 3.0.0 also concatenates protocol-relative header values into the /p/:pad/timeslider redirect in src/node/hooks/express/specialpages.ts. Exposure requires a deployment that lets client-supplied x-proxy-path reach Etherpad; shared caches can replay the poisoned admin response to later administrators, while the redirect issue is limited to phishing-style navigation to an attacker-controlled host.

CVSS severity6.1
Medium
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Etherpad before 3.1.0 allows remote attackers to run script in an administrator's browser via x-proxy-path. In src/node/hooks/express/admin.ts, Etherpad substitutes req.header('x-proxy-path') into /admin HTML, JavaScript, and CSS with replaceAll and no response variance controls; version 3.0.0 also concatenates protocol-relative header values into the /p/:pad/timeslider redirect in src/node/hooks/express/specialpages.ts. Exposure requires a deployment that lets client-supplied x-proxy-path reach Etherpad; shared caches can replay the poisoned admin response to later administrators, while the redirect issue is limited to phishing-style navigation to an attacker-controlled host.

The record

CVE
CVE-2026-55087
Published
Aug 19, 2026
Updated
Aug 19, 2026
Vendor
Etherpad Foundation
Product
Etherpad
Classifications
CWE-444, CWE-601, CWE-79, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2.1.0, < 3.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Etherpad Foundation · Etherpadversion=>= 2.1.0, < 3.1.0

Published CVSS scores

6.1GitLab Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CWE-601URL Redirection to Untrusted Site ('Open Redirect')
CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1189Drive-by Compromise

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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