CVE-2026-55090Network attack vector

Stored XSS via unescaped attribute values

Published Aug 19, 2026 · Updated Aug 20, 2026

Stored XSS in Etherpad before 3.3.0 allows remote authenticated users to run script in the Etherpad origin via HTML export. In getHTMLFromAtext, src/node/utils/ExportHtml.ts writes exportHtmlAdditionalTagsWithData hook output from the pad attribute pool into span data-* attributes without escaping the attribute value; the fix constrains the attribute name and escapes the value with Security.escapeHTMLAttribute. Exploitation requires editor-level control of pad content and a plugin path such as ep_font_color or ep_font_size that registers the hook, after which collaborators who open the export trigger script execution in the application origin.

CVSS severity8.7
High
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Etherpad before 3.3.0 allows remote authenticated users to run script in the Etherpad origin via HTML export. In getHTMLFromAtext, src/node/utils/ExportHtml.ts writes exportHtmlAdditionalTagsWithData hook output from the pad attribute pool into span data-* attributes without escaping the attribute value; the fix constrains the attribute name and escapes the value with Security.escapeHTMLAttribute. Exploitation requires editor-level control of pad content and a plugin path such as ep_font_color or ep_font_size that registers the hook, after which collaborators who open the export trigger script execution in the application origin.

The record

CVE
CVE-2026-55090
Published
Aug 19, 2026
Updated
Aug 20, 2026
Vendor
Etherpad Foundation
Product
Etherpad
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=< 3.3.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Etherpad Foundation · Etherpadversion=< 3.3.0

Published CVSS scores

5.4TenableCVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
8.7GitHub Advisory DatabaseCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript

Public exploit references

No public exploit references are available in this record.

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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