# CVE-2026-1721: agents XSS — Fixed in 0.3.10

📦 npm

Not in CISA KEV

# CVE-2026-1721 — agents

[Fix: cloudflare/agents#841](https://github.com/cloudflare/agents/pull/841)

CVE-2026-1721 is a Cross-site Scripting (XSS) vulnerability in agents. A fix is available for agents — see the affected versions and patch details below.

Reflected Cross-Site Scripting (XSS) vulnerability in AI Playground site

Also known as[GHSA-cvhv-6xm6-c3v4](/vulnerability/GHSA-cvhv-6xm6-c3v4)

Published

Feb 13, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

## Exploitation Status

### No confirmed exploitation observed yet

-   CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-1721.

## EPSS Exploitation Probability

[via FIRST.org ↗](https://www.first.org/epss/)

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs36th percentile — riskier than 36% of all scored CVEsHighest risk

0.00%0.31%0.61%0.92%0.0%0.4%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/).

## Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

300other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

`agents`npm

3.2Mdownloads / week

## 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) [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.
    

## Affected Packages

1 total 1 fixed

Ecosystem

Package

Vulnerable range

Fix

📦npm

`agents` 

all versions

0.3.10`npm install agents@0.3.10`

## Detection & mitigation playbook

Open-source dependency

1.  ### Detect
    
    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for agents, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
    
2.  ### Fix
    
    Update agents to 0.3.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-1721 is resolved across your whole dependency graph.
    
3.  ### Workarounds
    
    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
    

## Frequently Asked Questions

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, w

O3 Security · Impact-Aware SCA

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