Summary
GitHub MCP Server has Nil Pointer Dereference DoS in completion/complete Handler
A nil pointer dereference vulnerability in the GitHub MCP Server causes it to crash when receiving a malformed completion/complete request with missing or empty parameters. This allows any unauthenticated client to cause a complete denial of service.
Details
The CompletionsHandler function in pkg/github/server.go:198 accesses params.Ref without checking if it's nil first. When a client sends a completion/complete request with a missing ref field, the handler dereferences nil and the Go runtime panics.
The crash occurs before any authentication or token validation, so even requests with fake tokens can trigger it.
PoC
After completing the MCP initialization handshake, send either:
Empty params:
{"jsonrpc":"2.0","id":2,"method":"completion/complete","params":{}}
Missing ref field:
{"jsonrpc":"2.0","id":2,"method":"completion/complete","params":{"argument":{"name":"x","value":"y"}}}
Result:
panic: runtime error: invalid memory address or nil pointer dereference
goroutine 42 [running]:
github.com/github/github-mcp-server/pkg/github.NewMCPServer.CompletionsHandler.func1(...)
pkg/github/server.go:198 +0x24
Timeline
- Feb 21, 2026 - Initial report sent to [email protected]
- Mar 03, 2026 - Follow-up email sent, no response
- Mar 21, 2026 - Re-verified on v0.33.0, sent detailed report with PoC, no response
- Apr 06, 2026 - GHSA filed after 44 days without acknowledgment
Impact
Any unauthenticated client that can send JSON-RPC messages to the server can crash it immediately. This is a complete denial of service - the panic is unrecoverable and kills the process.
Automated fuzzing with mcpsec found 108 crashes out of 925 test cases (11.7% crash rate).
The application dereferences a null pointer, causing a crash. Typical impact: denial of service via crash.
CVE-2026-47427 has a CVSS score of 7.5 (High). The vector is network-reachable, no 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 (1.1.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
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.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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func (s *Server) CompletionsHandler(ctx context.Context, params *mcp.CompleteParams) (*mcp.CompleteResult, error) {
if params == nil || params.Ref == nil {
return nil, fmt.Errorf("invalid request: missing ref parameter")
}
// ... rest of handler
}
Frequently Asked Questions
- What is CVE-2026-47427? CVE-2026-47427 is a high-severity null pointer dereference vulnerability in github.com/github/github-mcp-server (go), affecting versions < 1.1.0. It is fixed in 1.1.0. The application dereferences a null pointer, causing a crash.
- How severe is CVE-2026-47427? CVE-2026-47427 has a CVSS score of 7.5 (High). 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.
- Which versions of github.com/github/github-mcp-server are affected by CVE-2026-47427? github.com/github/github-mcp-server (go) versions < 1.1.0 is affected.
- Is there a fix for CVE-2026-47427? Yes. CVE-2026-47427 is fixed in 1.1.0. Upgrade to this version or later.
- Is CVE-2026-47427 exploitable, and should I be worried? Whether CVE-2026-47427 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
- What actually determines whether CVE-2026-47427 is exploitable, and how bad it is? 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.
- How do I fix CVE-2026-47427? Upgrade
github.com/github/github-mcp-serverto 1.1.0 or later.