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CVE-2026-48529: GitHub MCP Server: Lockdown mode singleton in HTTP server causes cross-user GraphQL client confusion

• Severity: medium (CVSS 6.0 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-26 · updated 2026-10-25
• Weakness: CWE-284

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 products

• github-mcp-server: from 0.22.0, < 1.1.2

References

• https://github.com/github/github-mcp-server/security/advisories/GHSA-pjp5-fpmr-3349
• https://github.com/github/github-mcp-server/security/advisories/GHSA-pjp5-fpmr-3349

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