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CVE-2026-44429— MCP Registry: Stored XSS in catalogue UI via attribute-quote breakout in publisher-controlled `websiteUrl`

Quick assessment

Affected
modelcontextprotocol registry
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

MCP Registry是Model Context Protocol开源的一个MCP服务器应用商店。 MCP Registry 1.7.7之前版本存在跨站脚本漏洞，该漏洞源于公共目录UI，服务器端验证仅检查URL是否可解析、绝对且使用https方案，未拒绝引号字符，客户端通过innerHTML将值插值到双引号href属性中，escapeHtml助手未编码引号，导致攻击者可注入任意事件处理程序。

AI Predicted 8.2 Difficulty: Easy EPSS 0.24% · P14

Possible ATT&CK Techniques 1 AI

T1189 · Drive-by Compromise

Affected Version Matrix 1

VendorProduct Version RangeStatus
modelcontextprotocol registry < 1.7.7 affected
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I. Basic Information for CVE-2026-44429

Vulnerability Information
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Vulnerability Title
MCP Registry: Stored XSS in catalogue UI via attribute-quote breakout in publisher-controlled `websiteUrl`
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
MCP Registry 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
MCP Registry是Model Context Protocol开源的一个MCP服务器应用商店。 MCP Registry 1.7.7之前版本存在跨站脚本漏洞，该漏洞源于公共目录UI，服务器端验证仅检查URL是否可解析、绝对且使用https方案，未拒绝引号字符，客户端通过innerHTML将值插值到双引号href属性中，escapeHtml助手未编码引号，导致攻击者可注入任意事件处理程序。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
modelcontextprotocol registry < 1.7.7 -

II. Public POCs for CVE-2026-44429

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III. Intelligence Information for CVE-2026-44429

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Vendor Advisories for CVE-2026-44429 (1)

Same Patch Batch · modelcontextprotocol · 2026-05-14 · 6 CVEs total

CVE-2026-42559 8.8 HIGH RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport
CVE-2026-45781 3.5 LOW MCP Registry: OCI ownership validation fails open on upstream rate limits, allowing attack
CVE-2026-44430 MCP Registry: Unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-
CVE-2026-44427 MCP Registry: Open Redirect
CVE-2026-44428 MCP Registry: GitHub OIDC tokens replayable across registry deployments due to shared audi

IV. Related Vulnerabilities

Same product: registry
Same vendor: modelcontextprotocol
Same weakness: CWE-79

V. Comments for CVE-2026-44429

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