VBS-2026-0010CRITICALCVSS 9CWE-79

ShadowPrompt: trusted-origin extension chain enables injected prompts

A reported chain in the Claude browser extension combined permissive trusted-origin handling with DOM/XSS on a trusted subdomain, allowing prompt injection flows that appeared user-originated.

Published
2026-03-26
Discovered By
Koi Security
CVSS Score
9 / 10
Affected AI Platforms
Claude
Affected Tech Stack
Browser extension bridgesWildcard trusted originspostMessage channels
Remediation

Pin trusted origins narrowly, harden message origin validation, and enforce explicit approval boundaries before extension-driven assistant actions.

#claude#browser-extension#xss-chain#prompt-injection#origin-validation
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FAQ
Q

How do I check if my Browser extension bridges + Wildcard trusted origins app is affected by shadowPrompt: trusted-origin extension chain enables injected prompts?

A

A reported chain in the Claude browser extension combined permissive trusted-origin handling with DOM/XSS on a trusted subdomain, allowing prompt injection flows that appeared user-originated.. Search your codebase for Browser extension bridges, Wildcard trusted origins, postMessage channels patterns and verify the remediation has been applied. This is rated CVSS 9 — treat it as a live incident if your app is already in production.

Q

Why does Claude generate code with CWE-79 (critical severity)?

A

A reported chain in the Claude browser extension combined permissive trusted-origin handling with DOM/XSS on a trusted subdomain, allowing prompt injection flows that appeared user-originated.

Q

How do I fix shadowPrompt: trusted-origin extension chain enables injected prompts?

A

Pin trusted origins narrowly, harden message origin validation, and enforce explicit approval boundaries before extension-driven assistant actions.

Q

What can an attacker do if my app contains VBS-2026-0010?

A

With CVSS 9 (critical), this vulnerability is critical — an attacker can likely gain complete control of your data or infrastructure.