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CVE-2026-47427 high CVSS 7.5

Vulnerability in github.com/github/github-mcp-server (CVE-2026-47427)

Summary

Vulnerability in github.com/github/github-mcp-server (CVE-2026-47427). Risk of unauthorized operations or information disclosure. Exploitable via CompletionsHandler. Mitigation: upgrade to 1.1.0 or later.

Original description

The description as published by the source.

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).

T…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-47427 has been found in github.com/github/github-mcp-server.
Attackers can target a specific entry point like CompletionsHandler over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade github.com/github/github-mcp-server to 1.1.0 or later.
If unsure, ask your IT team or search "github.com/github/github-mcp-server CVE-2026-47427" on the vendor's site.

CVE-2026-47427 (github.com/github/github-mcp-server) — CWE-476 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: CompletionsHandler / params.Ref / ref
Patched: 1.1.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-476) exists in github.com/github/github-mcp-server. Attackers reach the vulnerable code path via CompletionsHandler without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/github/github-mcp-server. Attack surface: CompletionsHandler / params.Ref / ref.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.1.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/github/github-mcp-server' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'github.com/github/github-mcp-server' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で github.com/github/github-mcp-server を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade github.com/github/github-mcp-server to 1.1.0

    ステージング環境で 1.1.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

go github.com/github/github-mcp-server
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.1.0"}]}]

References

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