GitHub MCP Server 0.22.0-1.1.2 Auth Hijack via RepoAccessCache: CVE-2026-48529 June 2026

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

Vulnerability Analysis

CVE-2026-48529 can be exploited with network access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. Public availability of a proof of concept (POC) exploit exists for CVE-2026-48529. The potential impact of an exploit of this vulnerability is considered to be low. considered to have a small impact on confidentiality and integrity and availability.

Attack Vector:

NETWORK

Attack Complexity:

HIGH

Privileges Required:

LOW

User Interaction:

NONE

Scope:

CHANGED

Confidentiality Impact:

LOW

Integrity Impact:

LOW

Availability Impact:

LOW

Weakness Type

What is an Authorization Vulnerability?

The software does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

CVE-2026-48529 has been classified to as an Authorization vulnerability or weakness.

Products Associated with CVE-2026-48529

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Affected Versions

Exploit Probability

EPSS

0.14%

Percentile

3.70%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.