# 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.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:N/SI:L/SA:L`)
- **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:** Yes
- **Published:** 14 May 2026
- **Updated:** 15 May 2026
- **Also known as:** GHSA-rqv2-m695-f8j4, GO-2026-5637

## 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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-116 (Improper Encoding or Escaping of Output)

## 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 | Ecosystem | 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: Lfprojects Mcp Registry.

## How do I fix CVE-2026-44429?

Upgrade github.com/modelcontextprotocol/registry to 1.7.7 or later.

## 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

- [CVE-2026-44430](https://insights.sbomify.com/CVE-2026-44430/): MCP Registry has an unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, bypassing private-address allowlist (medium 6.3)
- [CVE-2026-44428](https://insights.sbomify.com/CVE-2026-44428/): MCP Registry: GitHub OIDC tokens replayable across registry deployments due to shared audience (low 2.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44429 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44429 exists.

Affected packages and fixed versions:
- github.com/modelcontextprotocol/registry (Go): affected all versions; fixed in 1.7.7
- github.com/modelcontextprotocol/registry (Go): affected all versions; fixed in 1.7.7
- github.com/modelcontextprotocol/registry (Go): affected all versions; fixed in 1.7.7

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-44429/ (Markdown: https://insights.sbomify.com/CVE-2026-44429/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44429
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44429
- OSV: https://osv.dev/vulnerability/CVE-2026-44429

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44429/
Summaries are generated and may contain mistakes; the official description above is the record.