OpenClaude's MCP OAuth Callback: State Check Bypass via error Param Leads to DoS
cve-program · CVE-2026-42073
PublishedOpenClaude 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.
Read the publisher's advisoryeuvd · EUVD-2026-33973
PublishedOpenClaude 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.
Read the publisher's advisorynvd · CVE-2026-42073
PublishedOpenClaude 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.
Read the publisher's advisoryosv · GHSA-c73c-x77g-854r
Published# 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. --- ## 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) - No authentication or prior knowledge of the `state` value is required --- ## Steps to Reproduce Save the following as `poc.js` and run with Node.js: ```javascript import { createServer } from 'http'; import { parse } from 'url'; const expectedState = "secure_state_abc123"; const server = createServer((req, res) => { const parsedUrl = parse(req.url || '', true); const { pathname, query } = parsedUrl; const { state, error } = query; if (pathname === '/callback') { // Vulnerable: error param causes state check to be skipped entirely if (!error && state !== expectedState) { res.writeHead(400); res.end('State mismatch'); console.log('[-] CSRF attempt blocked.'); return; } if (error) { res.writeHead(200); res.end(`Error: ${error}`); console.log(`[!] Server shutting down. Triggered by: ${error}`); server.close(); return; } } }); server.listen(12345, '127.0.0.1', () => { console.log('Listening on http://127.0.0.1:12345'); }); ``` **Terminal 1 — start the server:** ```bash node poc.js ``` **Terminal 2 — trigger the bypass:** ```bash curl "http://127.0.0.1:12345/callback?error=triggered" ``` **Expected result:** Server shuts down immediately. The `state` value was never checked. --- ## Root Cause The 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. --- ## Fix Move the `state` check before the `error` check, and remove the dependency on `!error`: ```typescript // Fixed if (state !== oauthState) { cleanup() rejectOnce(new Error('OAuth state mismatch - possible CSRF attack')) return } if (error) { cleanup() rejectOnce(new Error(errorMessage)) return } ``` With this change, any request — whether it contains an `error` parameter or not — must first pass the state validation before any further processing occurs. --- Credit: Xanlar Agamalizade
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cve-program · CVE-2026-42073
PublishedOpenClaude's MCP OAuth Callback: State Check Bypass via error Param Leads to DoS
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.
- Source published
- 2 Jun 2026 15:38:53 UTC
- Source modified
- 2 Jun 2026 17:40:55 UTC
- Saved here
- 23 Oct 2026 15:48:27 UTC
- Source terms
- CVE Program Terms of Use
Original source record · Cite this exact observation · Complete original publisher JSON
Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
euvd · EUVD-2026-33973
PublishedOpenClaude 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 …
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.
Additional publisher context
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
Original publisher date fields
datePublished: Jun 2, 2026, 3:38:53 PM
dateUpdated: Jun 2, 2026, 5:40:55 PM
- Source published
- Jun 2, 2026, 3:38:53 PM (timezone not stated)
- Source modified
- Jun 2, 2026, 5:40:55 PM (timezone not stated)
- Saved here
- 15 Nov 2026 13:03:26 UTC
- Source terms
- ENISA EUVD · source terms and attribution apply
Original source record · Cite this exact observation · Complete original publisher JSON
Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
EUVD CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
nvd · CVE-2026-42073
PublishedOpenClaude 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 …
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.
Additional publisher context
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Analyzed
Weakness classifications: CWE-352 · CWE-400
Original publisher date fields
published: 2026-06-02T17:16:31.910
lastModified: 2026-07-22T19:10:00.120
1 source CPE criteria · context only
- cpe:2.3:a:gitlawb:openclaude:*:*:*:*:*:*:*:*
The original JSON retains the logical configuration operators, exclusions and version bounds.
- Source published
- 2 Jun 2026 17:16:31 UTC
- Source modified
- 22 Jul 2026 19:10:00 UTC
- Saved here
- 25 Oct 2026 10:17:10 UTC
- Source terms
- NIST NVD usage terms; underlying source attribution retained
Original source record · Cite this exact observation · Complete original publisher JSON
Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS 3.1 · [email protected] · Secondary · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
osv · GHSA-c73c-x77g-854r
PublishedOpenClaude MCP OAuth Callback: State Check Bypass via error Param Leads to DoS
# 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. --- ## 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) - No authentication or prior knowledge of the `state` value is required --- ## Steps to Reproduce Save the following as `poc.js` and run with Node.js: ```javascript import { createServer } from 'http'; import { parse } from 'url'; const expectedState = "secure_state_abc123"; const server = createServer((req, res) => { const parsedUrl = parse(req.url || '', true); const { pathname, query } = parsedUrl; const { state, error } = query; if (pathname === '/callback') { // Vulnerable: error param causes state check to be skipped entirely if (!error && state !== expectedState) { res.writeHead(400); res.end('State mismatch'); console.log('[-] CSRF attempt blocked.'); return; } if (error) { res.writeHead(200); res.end(`Error: ${error}`); console.log(`[!] Server shutting down. Triggered by: ${error}`); server.close(); return; } } }); server.listen(12345, '127.0.0.1', () => { console.log('Listening on http://127.0.0.1:12345'); }); ``` **Terminal 1 — start the server:** ```bash node poc.js ``` **Terminal 2 — trigger the bypass:** ```bash curl "http://127.0.0.1:12345/callback?error=triggered" ``` **Expected result:** Server shuts down immediately. The `state` value was never checked. --- ## Root Cause The 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. --- ## Fix Move the `state` check before the `error` check, and remove the dependency on `!error`: ```typescript // Fixed if (state !== oauthState) { cleanup() rejectOnce(new Error('OAuth state mismatch - possible CSRF attack')) return } if (error) { cleanup() rejectOnce(new Error(errorMessage)) return } ``` With this change, any request — whether it contains an `error` parameter or not — must first pass the state validation before any further processing occurs. --- Credit: Xanlar Agamalizade
- Source published
- 12 May 2026 15:34:30 UTC
- Source modified
- 10 Sep 2026 03:51:05 UTC
- Saved here
- 24 Oct 2026 13:17:17 UTC
- Source terms
- GitHub Advisory Database · CC-BY-4.0
Original source record · Cite this exact observation · Complete original publisher JSON
Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Publisher rating · MODERATE