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 https://github.com/cloudflare/agents/pull/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.
CVSS
No CVSS.
References
| Link | Resource |
|---|---|
| https://github.com/cloudflare/agents/pull/841 |
Configurations
No configuration.
History
27 Feb 2026, 15:16
| Type | Values Removed | Values Added |
|---|---|---|
| CWE | CWE-79 |
13 Feb 2026, 03:15
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-02-13 03:15
Updated : 2026-02-27 15:16
NVD link : CVE-2026-1721
Mitre link : CVE-2026-1721
CVE.ORG link : CVE-2026-1721
JSON object : View
Products Affected
No product.
CWE
CWE-79
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')