OpenClaude MCP OAuth Callback: State Check Bypass via error Param Leads to DoS

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-42073: 0.26% estimated exploitation activity in the next 30 days; percentile 17.16 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: 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…

Published by the source

12 May 2026, 15:34 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 12:53 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c73c-x77g-854r

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-c73c-x77g-854r

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# Patch Next advisory brief: CVE-2026-42073

Advisory: OpenClaude MCP OAuth Callback: State Check Bypass via error Param Leads to DoS
IDs: CVE-2026-42073, GHSA-c73c-x77g-854r
Record: https://patchnext.com/advisories/cve-2026-42073 (revision 2, source checked 26 Oct 2026, 12:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @gitlawb/openclaude 0.5.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @gitlawb/openclaude: affected < 0.5.1; fixed in 0.5.1

## Suggested inspection (read-only)
- `npm ls @gitlawb/openclaude --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @gitlawb/openclaude.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-c73c-x77g-854r (OSV record GHSA-c73c-x77g-854r lists affected ranges: npm @gitlawb/openclaude >=0 <0.5.1 (fixed))
- Verified: https://github.com/advisories/GHSA-c73c-x77g-854r (GitHub-reviewed advisory GHSA-c73c-x77g-854r lists affected ranges: npm @gitlawb/openclaude >=0 <0.5.1)

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