CVE-2026-1721: agents · Cross-site Scripting
Affects agentsSource CVE Database V5
Not known to be exploited · CVSS 6.2 Medium : upgrade to 0.3.10 when convenient.
Data as of 25 Oct 2026, 19:02 UTC
- EPSS
- 0.4% chance of exploitation in 30 days – higher than 35% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 0.3.10
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:L/SA:NExploitation evidence
Disclosed: evidence found.
CVE published 13 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.
What to do
Upgrade agents to 0.3.10.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
GitHubagentspkg:github/agentsOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
To mitigate CVE-2026-1721, organizations and developers should immediately upgrade to agents-sdk version 0.3.10, which includes the necessary fixes to properly escape user-controlled input in the OAuth callback handler. For those maintaining custom OAuth callback implementations, it is critical to implement rigorous input validation and output encoding, especially escaping any data interpolated into inline script tags to prevent XSS. Employ Content Security Policy (CSP) headers that restrict script execution sources and disallow inline scripts where feasible to reduce the impact of potential XSS vulnerabilities. Additionally, implement security awareness training to educate users about the risks of clicking suspicious links, as exploitation requires user interaction. Regularly audit and test web applications for XSS vulnerabilities using automated scanners and manual penetration testing to identify and remediate similar issues proactively. Monitoring logs for unusual access patterns to MCP servers can help detect exploitation attempts early. Finally, maintain up-to-date dependencies and apply security patches promptly to minimize exposure.
Description
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.