Summary
The TrailingSlashMiddleware in internal/api/server.go is vulnerable to an open redirect attack. An attacker can craft a URL with a protocol-relative path (e.g., //evil.com/) that, after trailing slash removal, results in a Location header of //evil.com, which browsers interpret as an absolute URL to an external domain.
Details
The TrailingSlashMiddleware strips trailing slashes from request paths and issues a 308 Permanent Redirect to the cleaned path. However, it does not validate or sanitize the resulting path before using it as the redirect target.
When a request is made with a path like //evil.com/, the middleware processes it as follows:
PoC
- Start the registry server locally or identify a deployed instance
- Send a request with a double-slash path followed by an external domain:
curl -v https://<registry-host>//evil.com/
Impact
Phishing: Attackers can abuse the trusted registry domain to redirect users to credential-harvesting pages
Malware distribution: Redirect users to sites serving malicious downloads
Trust abuse: Links originating from the official MCP Registry domain carry implicit trust
Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.
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.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-44427? CVE-2026-44427 is a medium-severity open redirect vulnerability in github.com/modelcontextprotocol/registry (go), affecting versions >= 1.1.0, < 1.7.5. It is fixed in 1.7.5. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
- Which versions of github.com/modelcontextprotocol/registry are affected by CVE-2026-44427? github.com/modelcontextprotocol/registry (go) versions >= 1.1.0, < 1.7.5 is affected.
- Is there a fix for CVE-2026-44427? Yes. CVE-2026-44427 is fixed in 1.7.5. Upgrade to this version or later.
- Is CVE-2026-44427 exploitable, and should I be worried? Whether CVE-2026-44427 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-2026-44427 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-2026-44427? Upgrade
github.com/modelcontextprotocol/registryto 1.7.5 or later.