CVE-2026-48529 GitHub MCP Server: Lockdown mode singleton in HTTP server causes cross-user GraphQL client confusion
In HTTP lockdown mode, a singleton cache causes subsequent users' requests to execute using the first user's credentials, allowing unauthorized access.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-48529?
CVE-2026-48529 is a medium-severity authentication bypass vulnerability in github-mcp-server, published on 26 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
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.
Weakness: CWE-284
Which versions are affected by CVE-2026-48529?
3 open source packages ship an affected version, including github.com/github/github-mcp-server.
| Package | Affected | Fixed in |
|---|---|---|
github.com/github/github-mcp-server Go | From 0.22.0 | 1.1.2 |
github.com/github/github-mcp-server Go | From 0.22.0 | 1.1.2 |
github.com/github/github-mcp-server Go | From 0.22.0 | 1.1.2 |
How do I fix CVE-2026-48529?
Upgrade github.com/github/github-mcp-server to 1.1.2 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-48529 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48529 exists.
Sources
Also known as GHSA-pjp5-fpmr-3349, GO-2026-5779.