CVE-2026-48529 is a medium-severity security vulnerability in github.com/github/github-mcp-server (go), affecting versions >= 0.22.0, < 1.1.2. It is fixed in 1.1.2.
Summary 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. Details The singleton is defined in pkg/lockdown/lockdown.go: In HTTP mode, pkg/github/dependencies.go calls this per request: The singleton's internal client field is never updated after the first initialization. All lockdown GraphQL queries that check repository access and visibility (queryRepoAccessInfo, called by IsSafeContent) run under the first authenticated user's token for the lifetime of the process. IsSafeContent is called in at least six places across pkg/github/issues.go and pkg/github/pullrequests.go to decide whether to trust or sanitize content from external contributors. PoC The following program demonstrates that two distinct GraphQL clients produce the same singleton pointer, confirming that the second client is discarded: Output: <img width="1642" height="450" alt="image" src="https://github.com/user-attachments/assets/bec46420-9ba7-458e-8710-62f951cb836a" /> Impact This affects deployments running the HTTP server with --lockdown-mode, which is the intended configuration for multi-user scenarios such as GitHub Copilot's managed MCP endpoint. Three concrete consequences: First, the ViewerLogin field in cache entries always reflects the first authenticated user's identity. The IsSafeContent check repoInfo.ViewerLogin == strings.ToLower(username) compares this stale value against each subsequent user's login, producing incorrect results for all users except the first. Second, repository visibility and collaborator access data stored in the cache is evaluated through the first user's token. If user A cannot see a private repository but user B can (or vice versa), the cached isPrivate and hasPushAccess values will reflect user A's view of that repository, causing IsSafeContent to return wrong decisions for user B. In lockdown mode, a wrong true result means potentially injected content from untrusted external contributors is passed to the model without sanitization. Third, if the first user's token is revoked or expires, all subsequent lockdown GraphQL queries fail with authentication errors. Since getRepoAccessInfo propagates these errors, IsSafeContent returns an error for every request, breaking lockdown protection for all users until the process is restarted.
CVE-2026-48529 has a CVSS score of 6.0 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (1.1.2). Upgrading removes the vulnerable code path.
go
github.com/github/github-mcp-server (>= 0.22.0, < 1.1.2)github.com/github/github-mcp-server → 1.1.2 (go)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Already deployed Kodem? See CVE-2026-48529 in your environment →Upgrade github.com/github/github-mcp-server to 1.1.2 or later to resolve this vulnerability.
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CVE-2026-48529 is a medium-severity security vulnerability in github.com/github/github-mcp-server (go), affecting versions >= 0.22.0, < 1.1.2. It is fixed in 1.1.2.
CVE-2026-48529 has a CVSS score of 6.0 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
github.com/github/github-mcp-server (go) versions >= 0.22.0, < 1.1.2 is affected.
Yes. CVE-2026-48529 is fixed in 1.1.2. Upgrade to this version or later.
Whether CVE-2026-48529 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade github.com/github/github-mcp-server to 1.1.2 or later.