Cloudflare Agents has a Reflected Cross-Site Scripting (XSS) vulnerability in AI Playground site
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: https://github.com/cloudflare/agents/pull/841
- Agents-sdk users should upgrade to
agents@0.3.10 - Developers using
configureOAuthCallbackwith custom error handling in their own applications should ensure all user-controlled input is escaped before interpolation.
Credits
Disclosed responsibly by Nishant Kumawat
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | agents | < 0.3.10 | 0.3.10 |
References
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N- Weakness (CWE)
CWE-79- Platform
- npm
- Package
agents- Disclosed
- 13.02.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-w5cr-2qhr-jqc5 - CC BY 4.0
Vulnerability history: agents
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 02.2026 02.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Medium 3
Disclosures per year
- 2026: 3
-
Cloudflare Agents has a Reflected Cross-Site Scripting (XSS) vulnerability in AI Playground site this entry
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