{"id":"CVE-2026-42073","aliases":["EUVD-2026-33973","GHSA-c73c-x77g-854r"],"status":"published","title":"OpenClaude's MCP OAuth Callback: State Check Bypass via error Param Leads to DoS","description":"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.","severity":{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00255,"percentile":0.17233,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-352","CWE-400"],"published":"2026-05-12T15:34:30Z","modified":"2026-10-28T02:30:31Z","fixes":[{"ecosystem":"npm","package":"@gitlawb/openclaude","fixed_in":["0.5.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"@gitlawb/openclaude","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.5.1"}]}]},{"source":"osv","ecosystem":"npm","package":"@gitlawb/openclaude","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.5.1"}]}]}],"products":[{"vendor":"gitlawb","product":"openclaude"}],"references":[{"url":"https://github.com/Gitlawb/openclaude/security/advisories/GHSA-c73c-x77g-854r","tags":["x_refsource_CONFIRM","exploit","Exploit","Vendor Advisory","advisory","web"]},{"url":"https://github.com/Gitlawb/openclaude/commit/739b8d1f40fde0e401a5cbd2b9a55d88bd5124ad","tags":["x_refsource_MISC","Patch","fix","web"]},{"url":"https://github.com/Gitlawb/openclaude/releases/tag/v0.5.1","tags":["x_refsource_MISC","Release Notes","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42073","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-c73c-x77g-854r"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42073.json","tags":["advisory"]},{"url":"https://github.com/Gitlawb/openclaude","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-42073","title":"OpenClaude's MCP OAuth Callback: State Check Bypass via error Param Leads to DoS","description":"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.","status":"published","published":"2026-06-02T15:38:53.435Z","modified":"2026-06-02T17:40:55.678Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium","assessor":"cna"}],"cwes":["CWE-352","CWE-400"],"updated_at":"2026-11-02T13:40:23.731501Z"}],"euvd":[{"id":"EUVD-2026-33973","description":"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.","status":"published","published":"2026-06-02T15:38:53Z","modified":"2026-06-02T17:40:55Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"updated_at":"2026-11-02T18:20:55.651138Z"}],"ghsa":[{"id":"GHSA-c73c-x77g-854r","title":"OpenClaude MCP OAuth Callback: State Check Bypass via error Param Leads to DoS","description":"# OAuth State Validation Bypass via `error` Parameter Causes Local Server DoS in MCP Auth Callback\n---\n\n## Description\n\nThe 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.\n\nThe vulnerable code looks like this:\n\n```typescript\nif (!error \u0026\u0026 state !== oauthState) {\n    rejectOnce(new Error('OAuth state mismatch - possible CSRF attack'))\n    return\n}\n\nif (error) {\n    cleanup()\n    rejectOnce(new Error(errorMessage))\n    return\n}\n```\n\nWhen 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.\n\nThe attacker does not need to know the `state` value. Any request containing an `error` parameter is enough to trigger the shutdown.\n\n---\n\n## Impact\n\n- The user's OAuth flow is silently terminated mid-session\n- The local callback server is shut down (Denial of Service)\n- Can be triggered remotely via a malicious web page using a cross-origin request (CSRF)\n- No authentication or prior knowledge of the `state` value is required\n\n---\n\n## Steps to Reproduce\n\nSave the following as `poc.js` and run with Node.js:\n\n```javascript\nimport { createServer } from 'http';\nimport { parse } from 'url';\n\nconst expectedState = \"secure_state_abc123\";\n\nconst server = createServer((req, res) =\u003e {\n    const parsedUrl = parse(req.url || '', true);\n    const { pathname, query } = parsedUrl;\n    const { state, error } = query;\n\n    if (pathname === '/callback') {\n\n        // Vulnerable: error param causes state check to be skipped entirely\n        if (!error \u0026\u0026 state !== expectedState) {\n            res.writeHead(400);\n            res.end('State mismatch');\n            console.log('[-] CSRF attempt blocked.');\n            return;\n        }\n\n        if (error) {\n            res.writeHead(200);\n            res.end(`Error: ${error}`);\n            console.log(`[!] Server shutting down. Triggered by: ${error}`);\n            server.close();\n            return;\n        }\n    }\n});\n\nserver.listen(12345, '127.0.0.1', () =\u003e {\n    console.log('Listening on http://127.0.0.1:12345');\n});\n```\n\n**Terminal 1 — start the server:**\n```bash\nnode poc.js\n```\n\n**Terminal 2 — trigger the bypass:**\n```bash\ncurl \"http://127.0.0.1:12345/callback?error=triggered\"\n```\n\n**Expected result:** Server shuts down immediately. The `state` value was never checked.\n\n---\n\n## Root Cause\n\nThe CSRF protection is conditioned on `!error`, meaning it is silently disabled whenever an `error` parameter is present. The two checks need to be decoupled — state validation must happen first, independently of any other parameters.\n\n---\n\n## Fix\n\nMove the `state` check before the `error` check, and remove the dependency on `!error`:\n\n```typescript\n// Fixed\nif (state !== oauthState) {\n    cleanup()\n    rejectOnce(new Error('OAuth state mismatch - possible CSRF attack'))\n    return\n}\n\nif (error) {\n    cleanup()\n    rejectOnce(new Error(errorMessage))\n    return\n}\n```\n\nWith this change, any request — whether it contains an `error` parameter or not — must first pass the state validation before any further processing occurs.\n\n---\n\nCredit: Xanlar Agamalizade","status":"published","published":"2026-05-12T15:34:30Z","modified":"2026-06-09T10:59:33Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"cwes":["CWE-352","CWE-400"],"updated_at":"2026-11-02T14:40:23.739691Z"}],"nvd":[{"id":"CVE-2026-42073","description":"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.","status":"published","published":"2026-06-02T17:16:31.91Z","modified":"2026-07-22T19:10:00.12Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium","assessor":"secondary"}],"cwes":["CWE-352","CWE-400"],"updated_at":"2026-11-02T14:12:22.022466Z"}],"osv":[{"id":"CVE-2026-42073","title":"OpenClaude's MCP OAuth Callback: State Check Bypass via error Param Leads to DoS","description":"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.","status":"published","published":"2026-06-02T15:38:53.435Z","modified":"2026-10-28T02:30:31.022697001Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"cwes":["CWE-352","CWE-400"],"updated_at":"2026-11-02T15:45:04.117819Z"},{"id":"GHSA-c73c-x77g-854r","title":"OpenClaude MCP OAuth Callback: State Check Bypass via error Param Leads to DoS","description":"# OAuth State Validation Bypass via `error` Parameter Causes Local Server DoS in MCP Auth Callback\n---\n\n## Description\n\nThe 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.\n\nThe vulnerable code looks like this:\n\n```typescript\nif (!error \u0026\u0026 state !== oauthState) {\n    rejectOnce(new Error('OAuth state mismatch - possible CSRF attack'))\n    return\n}\n\nif (error) {\n    cleanup()\n    rejectOnce(new Error(errorMessage))\n    return\n}\n```\n\nWhen 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.\n\nThe attacker does not need to know the `state` value. Any request containing an `error` parameter is enough to trigger the shutdown.\n\n---\n\n## Impact\n\n- The user's OAuth flow is silently terminated mid-session\n- The local callback server is shut down (Denial of Service)\n- Can be triggered remotely via a malicious web page using a cross-origin request (CSRF)\n- No authentication or prior knowledge of the `state` value is required\n\n---\n\n## Steps to Reproduce\n\nSave the following as `poc.js` and run with Node.js:\n\n```javascript\nimport { createServer } from 'http';\nimport { parse } from 'url';\n\nconst expectedState = \"secure_state_abc123\";\n\nconst server = createServer((req, res) =\u003e {\n    const parsedUrl = parse(req.url || '', true);\n    const { pathname, query } = parsedUrl;\n    const { state, error } = query;\n\n    if (pathname === '/callback') {\n\n        // Vulnerable: error param causes state check to be skipped entirely\n        if (!error \u0026\u0026 state !== expectedState) {\n            res.writeHead(400);\n            res.end('State mismatch');\n            console.log('[-] CSRF attempt blocked.');\n            return;\n        }\n\n        if (error) {\n            res.writeHead(200);\n            res.end(`Error: ${error}`);\n            console.log(`[!] Server shutting down. Triggered by: ${error}`);\n            server.close();\n            return;\n        }\n    }\n});\n\nserver.listen(12345, '127.0.0.1', () =\u003e {\n    console.log('Listening on http://127.0.0.1:12345');\n});\n```\n\n**Terminal 1 — start the server:**\n```bash\nnode poc.js\n```\n\n**Terminal 2 — trigger the bypass:**\n```bash\ncurl \"http://127.0.0.1:12345/callback?error=triggered\"\n```\n\n**Expected result:** Server shuts down immediately. The `state` value was never checked.\n\n---\n\n## Root Cause\n\nThe CSRF protection is conditioned on `!error`, meaning it is silently disabled whenever an `error` parameter is present. The two checks need to be decoupled — state validation must happen first, independently of any other parameters.\n\n---\n\n## Fix\n\nMove the `state` check before the `error` check, and remove the dependency on `!error`:\n\n```typescript\n// Fixed\nif (state !== oauthState) {\n    cleanup()\n    rejectOnce(new Error('OAuth state mismatch - possible CSRF attack'))\n    return\n}\n\nif (error) {\n    cleanup()\n    rejectOnce(new Error(errorMessage))\n    return\n}\n```\n\nWith this change, any request — whether it contains an `error` parameter or not — must first pass the state validation before any further processing occurs.\n\n---\n\nCredit: Xanlar Agamalizade","status":"published","published":"2026-05-12T15:34:30Z","modified":"2026-09-10T03:51:05.297595464Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"cwes":["CWE-352","CWE-400"],"updated_at":"2026-11-02T15:46:44.571161Z"}]}}