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Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-55090

MEDIUM · 5.3 CVSS v4.0 Published 2026-08-19
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
60/100
Remediation priority · Elevated
Remotely reachable No privileges Patch available 6 days old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Etherpad is a real-time collaborative editor. Prior to 3.3.0, getHTMLFromAtext in src/node/utils/ExportHtml.ts interpolates values from the exportHtmlAdditionalTagsWithData plugin hook into span data attributes without HTML attribute escaping. A pad editor can place an attacker-controlled value into the attribute pool through moveOpsToNewPool and AttributePool.putAttrib. When a bundled plugin such as ep_font_color or ep_font_size registers the hook, opening the resulting HTML export causes the value to execute as stored cross-site scripting in the Etherpad origin. This issue is fixed in version 3.3.0.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-79

Untrusted input is placed into a web page without being neutralised, so an attacker's markup or script executes in another user's browser. That can hijack sessions, capture keystrokes, or silently perform actions as the victim. Fixing it properly means context-aware output encoding everywhere data meets HTML, backed by a content-security policy as a second line of defence.

General guidance for the cross-site scripting (xss) class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
P
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Recommended fix High confidence

Etherpad version 3.3.0

  1. 1. Back up your current Etherpad installation including all configuration files and database/pad data.
  2. 2. Identify your current Etherpad version by checking the package.json or running the equivalent version command.
  3. 3. Consult the Etherpad upgrade documentation for your deployment method (npm, Docker, etc.).
  4. 4. Upgrade to version 3.3.0 or later. For npm installations, run: npm install [email protected] (or specify the latest stable version).
  5. 5. For Docker deployments, pull the updated image tag corresponding to version 3.3.0 or later.
  6. 6. Restore your configuration and verify the installation completed successfully.
  7. 7. Test the HTML export functionality with plugins like ep_font_color or ep_font_size to confirm the XSS vulnerability is no longer present.
  8. 8. Monitor application logs for any errors during startup and operation.
Caveat Review the Etherpad 3.3.0 release notes for any breaking changes; minor version upgrades typically have low risk but may include API or configuration changes

Generated from the published advisory — verify against the referenced sources before acting.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-55090 in production — separate from our analysis above.

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