Vulnerability · Published Jun 26, 2026 · Assigned by GitHub_M
CVE-2026-48529GitHub MCP Server: Lockdown mode singleton in HTTP server causes cross-user GraphQL client confusion
Medium 6.0
In plain English
A medium-severity improper access control in github-mcp-server from github. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 6% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
GitHub MCP Server is GitHub's official MCP Server. From 0.22.0 until 1.1.2, when running in HTTP mode with --lockdown-mode enabled, the RepoAccessCache is implemented as a process-global singleton initialized with the first authenticated user's GraphQL client. All subsequent requests from different users share this singleton and their lockdown-related GraphQL queries are executed using the first user's credentials. The singleton is never updated to reflect later users' tokens. This vulnerability is fixed in 1.1.2.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/github/github-mcp-server | 1.1.2 | GHSA-pjp5-fpmr-3349 |
| Go | github.com/github/github-mcp-server | 1.1.2 | GO-2026-5779 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| github | github-mcp-server | >= 0.22.0, < 1.1.2 |
Weakness: CWE-284 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L