MediumVulnerability
CVE-2026-1721: AI Playground reflected XSS through OAuth callback error parameter
- Source
- NVD(opens in a new tab)
- Identifier
- CVE-2026-1721
- Published
- Record updated
- Affected
- agents < 0.3.10
- Fixed in
- 0.3.10
- released February 4, 2026, 9 days before disclosure
- Known exploitation
- Not listed in the CISA Known Exploited Vulnerabilities catalog at the last check.
- EPSS
- 0.4%
Summary
A reflected XSS flaw in the AI Playground's OAuth callback handler (`site/ai-playground/src/server.ts`) interpolates the `error_description` query parameter into an inline `<script>` tag without escaping. A victim who clicks a crafted link lets an attacker run arbitrary JavaScript in their session, exposing stored LLM chat history and allowing actions on any MCP servers connected to that session, public or authenticated.
Mitigation
Agents-sdk users should upgrade to agents@0.3.10. Developers using configureOAuthCallback with custom error handling should escape all user-controlled input before interpolation. The source also links PR https://github.com/cloudflare/agents/pull/841.
Topics
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