TI-2026-35889 Aliases CVE-2026-48529 GHSA-pjp5-fpmr-3349

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

MEDIUM 60CWE-284Published 2026-06-26 · Updated 2026-06-27

Key facts

Attack vector: Network
Privileges required: Low
User interaction: None
Attack complexity: High
Impact type: Security bypass
Confidentiality · integrity · availability: Low · Low · Low
Fix status: Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-284.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00166 5th percentileScored 2026-11-07

Fix Fixed github-mcp-server (github): 1.1.2github.com/github/github-mcp-server (Go): 1.1.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
GitHub	github-mcp-server	0.22.0 to before 1.1.2	1.1.2	Patch available	CNA
—	github.com/github/github-mcp-server (Go)	0.22.0 to before 1.1.2	1.1.2	Patch available	GHSA-pjp5-fpmr-3349

github-mcp-server VendorGitHub Affected 0.22.0 to before 1.1.2 Fixed in 1.1.2 Patch available CNA
github.com/github/github-mcp-server (Go) Vendor— Affected 0.22.0 to before 1.1.2 Fixed in 1.1.2 Patch available GHSA-pjp5-fpmr-3349

Remediation

Fix · CNA github-mcp-server (github) Fixed in 1.1.2
Fix · GHSA-pjp5-fpmr-3349 github.com/github/github-mcp-server (Go) Fixed in 1.1.2 Advisory →

Timeline

2026-10-02 Threatist record created from CVE-2026-48529
2026-10-03 Alias added: GHSA-pjp5-fpmr-3349

References

Other 2

TI-2024-04632 An authentication bypass vulnerability was present in the GitHub Enterprise Server (GHES)… CVSS 4.0CRITICAL 10.0
TI-2024-00181 Unsafe Reflection in Github Enterprise Server leading to Command Injection CVSS 3.1CRITICAL 9.8
TI-2024-00466 Privilege Escalation by Code Injection in the Management Console in GitHub Enterprise Server CVSS 3.1HIGH 8.8
TI-2022-08539 Integer overflow in table parsing extension leads to heap memory corruption CVSS 3.1CRITICAL 9.8
TI-2026-34990 GitHub MCP Server: Nil Pointer Dereference DoS in completion/complete Handler CVSS 3.1HIGH 7.5
TI-2026-32884 GitHub Copilot CLI: Nested Bare Repository Can Execute Arbitrary Commands via core.fsmonitor CVSS 4.0HIGH 8.5

See all 178 →

Sources

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