OAuth session interruption via error parameter bypass
Published Jun 2, 2026 · Updated Jun 2, 2026
CSRF in OpenClaude before 0.5.1 allows remote attackers to interrupt an active MCP OAuth flow via a crafted callback request. In src/services/mcp/auth.ts, the callback handler conditions state validation on the absence of an error parameter, then calls cleanup when that parameter is present. A malicious web page can send the cross-origin request without authentication or the secret state, but an OAuth flow must be active; the result is termination of that session and shutdown of its temporary loopback server.
Summary
What happened
CSRF in OpenClaude before 0.5.1 allows remote attackers to interrupt an active MCP OAuth flow via a crafted callback request. In src/services/mcp/auth.ts, the callback handler conditions state validation on the absence of an error parameter, then calls cleanup when that parameter is present. A malicious web page can send the cross-origin request without authentication or the secret state, but an OAuth flow must be active; the result is termination of that session and shutdown of its temporary loopback server.
The record
- CVE
- CVE-2026-42073
- Published
- Jun 2, 2026
- Updated
- Jun 2, 2026
- Vendor
- Gitlawb
- Product
- OpenClaude
- Classifications
- CWE-400, CWE-352, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 2, 2026CVE publishedPublication date reported by the CVE source.
- Jun 2, 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.
- Affected versionversion=< 0.5.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
- Vendor-advisory OAuth callback shutdown proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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