How severe is CVE-2026-44427?

No CVSS score has been assigned to CVE-2026-44427 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-44427?

CVE-2026-44427 affects the following packages: github.com/modelcontextprotocol/registry (Go). Ecosystems affected: Go.

How do I fix CVE-2026-44427?

Update github.com/modelcontextprotocol/registry to 1.7.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44427 is resolved across your whole dependency graph.

How do I detect CVE-2026-44427 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/modelcontextprotocol/registry, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-44427 if there is no patch (or I can't update yet)?

Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.

Is CVE-2026-44427 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-44427 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-44427?

CVE-2026-44427 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 41th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-44427?

CVE-2026-44427 is classified as Open Redirect (CWE-601). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-44427 published, and has it been updated?

CVE-2026-44427 was published on May 14, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

CVE-2026-44427 — registry

Fix: modelcontextprotocol/registry#1227

CVE-2026-44427 is a Open Redirect vulnerability in github.com/modelcontextprotocol/registry. A fix is available for github.com/modelcontextprotocol/registry — see the affected versions and patch details below.

MCP Registry: Open Redirect

Also known asGHSA-v8vw-gw5j-w7m6GO-2026-5658

Published

May 14, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44427.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐹github.com/modelcontextprotocol/registry

Real-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

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/ <img width="3066" height="969" alt="image" src="https://github.com/user-attachments/assets/a5305f00-29bf-4708-952a-478d608f2074" />
Observe the 308 Permanent Redirect response with Location: //evil.com:
When accessed in a browser, the user is redirected to https://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

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/modelcontextprotocol/registry`	≥ 1.1.0&&< 1.7.5	1.7.5`go get github.com/modelcontextprotocol/registry@v1.7.5`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/modelcontextprotocol/registry, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/modelcontextprotocol/registry to 1.7.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44427 is resolved across your whole dependency graph.
Workarounds
Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.

Frequently Asked Questions

### 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

O3 Security · Impact-Aware SCA

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