GHSA-w4q6-qw23-4rg7 is a high-severity (CVSS 7.5) NULL Pointer Dereference vulnerability in github.com/github/github-mcp-server. O3 Security confirms whether GHSA-w4q6-qw23-4rg7 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
GitHub MCP Server has Nil Pointer Dereference DoS in completion/complete Handler
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-w4q6-qw23-4rg7.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-w4q6-qw23-4rg7 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 372,324 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/github/github-mcp-serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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
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).
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
Suggested Fix
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
}
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/github/github-mcp-server | all versions | 1.1.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/github/github-mcp-server. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/github/github-mcp-server to 1.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-w4q6-qw23-4rg7 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-w4q6-qw23-4rg7 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-w4q6-qw23-4rg7. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-w4q6-qw23-4rg7 in your dependencies?
O3 detects GHSA-w4q6-qw23-4rg7 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.