CVE-2026-1721Network attack vector

Session script execution via unescaped OAuth error

Published Feb 13, 2026 · Updated Feb 13, 2026

Reflected XSS in Cloudflare Agents before 0.3.10 allows remote attackers to execute JavaScript through an OAuth callback error. The AI Playground callback in site/ai-playground/src/server.ts inserts error_description into an inline script without escaping it. Exploitation requires a victim to open a crafted link; the script runs in that session and can read chat history or use connected MCP servers.

CVSS severity6.2
Medium
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in Cloudflare Agents before 0.3.10 allows remote attackers to execute JavaScript through an OAuth callback error. The AI Playground callback in site/ai-playground/src/server.ts inserts error_description into an inline script without escaping it. Exploitation requires a victim to open a crafted link; the script runs in that session and can read chat history or use connected MCP servers.

The record

CVE
CVE-2026-1721
Published
Feb 13, 2026
Updated
Feb 13, 2026
Vendor
Cloudflare
Product
Cloudflare Agents
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 13, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <0.3.10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cloudflare · Cloudflare Agentsversion=0 <0.3.10

Published CVSS scores

7.1GitLab Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N
6.2GitHub Advisory DatabaseCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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