CVE-2026-1721: Agents Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-cvhv-6xm6-c3v4
Share
CWE-79
Published
Advisory Summary

CVE-2026-1721 is a MODERATE cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Agents libraries in the npm ecosystem. The issue involves cloudflare agents is vulnerable to reflected cross-site scripting in the ai playground's oauth callback handler. Remediation is available by upgrading affected packages to version 0.3.10.

CVE-2026-1721 at a Glance

CVE Identifier CVE-2026-1721
GHSA Identifier GHSA-cvhv-6xm6-c3v4
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Agents
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-1721

To remediate this vulnerability, upgrade all affected Agents dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

agents fixed: 0.3.10 
npm install agents@0.3.10
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls agents

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-1721, inspect your project dependencies using npm:

npm ls agents

Analyze the terminal output to locate any version of Agents in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.3.10), your application is affected.

Note: The npm ls agents command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Agents, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-1721 Affected Agents Versions

1 component(s)
Fixed Versions:
0.3.10
Product / Package Ecosystem Affected Versions Fixed Version
agents
npm/agents
npm
< 0.3.10
0.3.10

References

NVD — CVE-2026-1721 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-1721
Agents Source Repository REPOSITORY
https://github.com/cloudflare/agents/pull/841
Security Fix Commit FIX COMMIT
https://github.com/cloudflare/agents/commit/3f490d045844e4884db741afbb66ca1fe65d4093
Agents Source Repository REPOSITORY
https://github.com/cloudflare/agents

Frequently Asked Questions

What is CVE-2026-1721?
CVE-2026-1721 is a security vulnerability in Agents involving Cloudflare Agents is Vulnerable to Reflected Cross-Site Scripting in the AI Playground's OAuth callback handler under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Agents versions are affected?
Affected versions include releases prior to 0.3.10 across affected packages: agents.
What version fixes CVE-2026-1721?
Upgrading to 0.3.10 (or the latest patched release for your respective branch) resolves the vulnerability.
Is agents affected?
Yes, agents is affected in releases prior to 0.3.10. Upgrade your dependency to 0.3.10 or later.
What CWE is associated with CVE-2026-1721?
CVE-2026-1721 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check npm dependencies for CVE-2026-1721?
Run the dependency tree command: 'npm ls agents'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-cvhv-6xm6-c3v4",
  "modified" : "2026-02-13T20:04:56Z",
  "published" : "2026-02-13T03:31:23Z",
  "aliases" : [ "CVE-2026-1721" ],
  "summary" : "Cloudflare Agents is Vulnerable to Reflected Cross-Site Scripting in the AI Playground's OAuth callback handler",
  "details" : "Summary\n\nA 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.\n\nRoot cause\n\nThe 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.\n\nImpact\n\nAn attacker could craft a malicious link that, when clicked by a victim, would:\n\n  *  Steal user chat message history - Access all LLM interactions stored in the user's session.\n\n\n  *  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\n\n\nMitigation:\n\n  *  PR:  https://github.com/cloudflare/agents/pull/841 https://github.com/cloudflare/agents/pull/841 \n  *  Agents-sdk users should upgrade to agents@0.3.10\n  *  Developers using configureOAuthCallback with custom error handling in their own applications should ensure all user-controlled input is escaped before interpolation.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "agents"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.3.10"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-1721"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cloudflare/agents/pull/841"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cloudflare/agents/commit/3f490d045844e4884db741afbb66ca1fe65d4093"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/cloudflare/agents"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-13T20:04:55Z",
    "nvd_published_at" : "2026-02-13T03:15:52Z"
  }
}