CVE-2026-45781: modelcontextprotocol registry Failing Open

Vulnerability summary

CVE-2026-45781 is a low (CVSS 3.5) Failing Open vulnerability in modelcontextprotocol registry. EPSS estimates a 0.25% chance of exploitation in the next 30 days, higher than 15.2% of scored vulnerabilities.

Timeline

1. 14-05-2026
   PublishedVulnerability first disclosed.
2. 16-05-2026
   Last modifiedVulnerability information updated.

Description

The MCP Registry provides MCP clients with a list of MCP servers, like an app store for MCP servers. Prior to 1.7.9, OCI ownership validation skips label-match check when upstream OCI registry returns HTTP 429, letting any authenticated publisher bind their io.github.<user>/* namespace to OCI images they do not control. internal/validators/registries/oci.go:104-119 fails open on http.StatusTooManyRequests: when the registry's anonymous fetch to the upstream OCI registry is rate-limited, ValidateOCI returns nil and the publish is accepted without ever running the io.modelcontextprotocol.server.name label-match check at lines 122-141. That label check is the only cross-system ownership proof the registry applies to OCI packages — every other registry type (NPM, PyPI, NuGet, MCPB) treats a non-200 upstream response as a hard error. This vulnerability is fixed in 1.7.9.

• CWE-636Not Failing Securely ('Failing Open')When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions.