Packages / agents / Security

ModerateVulnerabilityGHSA-w5cr-2qhr-jqc5Published 13 Feb 2026

Cloudflare Agents has a Reflected Cross-Site Scripting (XSS) vulnerability in AI Playground site

Affected releases · agents

  • 0.3.x0.3.0 – 0.3.9Fixed in 0.3.10
  • 0.2.x0.2.0 – 0.2.35No fix on this line yet
  • 0.1.x and older0.0.1 – 0.1.6No fix, no longer updated

On 0.3.x, the newest line:

npm install agents@0.3.10

  1. Affected

    0.0.1 – 0.3.9

    130 releases

  2. Fixed

    0.3.10 – 0.29.0

    75 releases, latest

205 stable releases of agents, oldest to newest.

Is your project affected?

Paste your package.json, or type the range you declare for agents. It is read in your browser and sent nowhere.

What happens

Summary

A Reflected Cross-Site Scripting (XSS) vulnerability was discovered in the AI Playground's OAuth callback handler. The error_description query parameter was directly interpolated into an HTML script tag without proper escaping, allowing attackers to execute arbitrary JavaScript in the context of the victim's session.

Root cause

The OAuth callback handler in site/ai-playground/src/server.ts directly interpolated the authError value, sourced from the error_description query parameter, into an inline <script> tag.

Impact

An attacker could craft a malicious link that, when clicked by a victim, would:

  • Steal user chat message history

  • Access all LLM interactions stored in the user's session.

  • Access connected MCP Servers

  • Interact with any MCP servers connected to the victim's session (public or authenticated/private), potentially allowing the attacker to perform actions on the victim's behalf

Mitigation:

  • PR: #841

  • Agents-sdk users should upgrade to agents@0.3.10

  • Developers using configureOAuthCallback with custom error handling in their own applications should ensure all user-controlled input is escaped before interpolation.

Credits

Disclosed responsibly by Nishant Kumawat