modelcontextprotocol registry up to 1.7.6 ui_index.html cross site scripting

Summaryinfo

A vulnerability has been found in modelcontextprotocol registry up to 1.7.6 and classified as problematic. Impacted is an unknown function of the file internal/api/handlers/v0/ui_index.html. Performing a manipulation results in cross site scripting. This vulnerability is reported as CVE-2026-44429. The attack is possible to be carried out remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as problematic, was found in modelcontextprotocol registry up to 1.7.6. This affects an unknown part of the file internal/api/handlers/v0/ui_index.html. The manipulation with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. This is going to have an impact on integrity. The summary by CVE is:

The MCP Registry provides MCP clients with a list of MCP servers, like an app store for MCP servers. Prior to 1.7.7, the public catalogue UI served at GET / (file internal/api/handlers/v0/ui_index.html) is vulnerable to stored cross-site scripting via the server.websiteUrl field of any published server.json. Server-side validation in internal/validators/validators.go (validateWebsiteURL) only checks that the URL parses, is absolute, and uses the https scheme; it does not reject quote characters. Client-side, the value is interpolated into a double-quoted href attribute via innerHTML, using a homegrown escapeHtml helper that performs the standard textContent → innerHTML round-trip. Per the HTML serialisation algorithm, that round-trip encodes only &, <, > and U+00A0 inside text nodes — it does not encode " or '. A literal " in websiteUrl therefore breaks out of the href attribute, allowing arbitrary on* event handlers to be appended to the same <a> element. The Content-Security-Policy on / is script-src 'self' 'unsafe-inline' https://cdn.tailwindcss.com, so the injected event handlers execute. Any user able to obtain a publish token (e.g. via POST /v0/auth/github-at with their own GitHub account, or POST /v0/auth/none on a deployment that has anonymous auth enabled) can plant a poisoned record visible to every visitor of the registry homepage. This vulnerability is fixed in 1.7.7.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-44429 since 05/06/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

By approaching the search of inurl:internal/api/handlers/v0/ui_index.html it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 1.7.7 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• modelcontextprotocol

Name

• registry

Version

• 1.7.0
• 1.7.1
• 1.7.2
• 1.7.3
• 1.7.4
• 1.7.5
• 1.7.6

Website

• Product: https://github.com/modelcontextprotocol/registry/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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