EUVD-2026-324072

fkie_cve-2026-42073

OpenClaude is an open-source coding-agent command line interface for cloud and local model providers. Prior to version 0.5.1, the OpenClaude MCP authentication flow starts a temporary local HTTP server to handle OAuth callbacks. To prevent CSRF attacks, the server validates a state parameter against an internally stored value. However, due to a logic flaw in the order of conditionals, an attacker can completely bypass this check and force the server to shut down — without knowing the state value at all. This issue has been patched in version 0.5.1.

GHSA-c73c-x77g-854r — OpenClaude MCP OAuth Callback: State Check Bypass via error Param Leads to DoS

Affected: npm: @gitlawb/openclaude

# OAuth State Validation Bypass via `error` Parameter Causes Local Server DoS in MCP Auth Callback ---

## Description

The OpenClaude MCP authentication flow starts a temporary local HTTP server to handle OAuth callbacks. To prevent CSRF attacks, the server validates a `state` parameter against an internally stored value. However, due to a logic flaw in the order of conditionals, an attacker can completely bypass this check and force the server to shut down — without knowing the `state` value at all.

The vulnerable code looks like this:

```typescript if (!error && state !== oauthState) { rejectOnce(new Error('OAuth state mismatch - possible CSRF attack')) return }

if (error) { cleanup() rejectOnce(new Error(errorMessage)) return } ```

When a request arrives with an `error` query parameter (e.g., `?error=anything`), the first condition becomes `false` because `!error` evaluates to `false`. This means the CSRF check is **never reached**. Execution falls through to the second block, where `cleanup()` is called — shutting down the local server and terminating the user's active authentication session.

The attacker does not need to know the `state` value. Any request containing an `error` parameter is enough to trigger the shutdown.

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## Impact

- The user's OAuth flow is silently terminated mid-session - The local callback server is shut down (Denial of Service) - Can be triggered remotely via a malicious web page using a cross-origin request (CSRF)…

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EUVD-2026-324072

fkie_cve-2026-42073

GHSA-c73c-x77g-854r — OpenClaude MCP OAuth Callback: State Check Bypass via error Param Leads to DoS