CVE-2026-44429 MCP Registry: Stored XSS in catalogue UI via attribute-quote breakout in publisher-controlled `websiteUrl`
Attackers can inject malicious scripts into the MCP Registry homepage via the websiteUrl field, potentially compromising user sessions and executing code in browsers.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-44429?
CVE-2026-44429 is a medium-severity cross-site scripting vulnerability in modelcontextprotocol registry, published on 14 May 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
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.
Which versions are affected by CVE-2026-44429?
3 open source packages ship an affected version, including github.com/modelcontextprotocol/registry. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/modelcontextprotocol/registry Go | All versions | 1.7.7 |
github.com/modelcontextprotocol/registry Go | All versions | 1.7.7 |
github.com/modelcontextprotocol/registry Go | All versions | 1.7.7 |
Products include Lfprojects Mcp Registry.
How do I fix CVE-2026-44429?
Upgrade github.com/modelcontextprotocol/registry to 1.7.7 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-44429 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44429 exists.
Other vulnerabilities in modelcontextprotocol registry
Sources
Also known as GHSA-rqv2-m695-f8j4, GO-2026-5637.