{"id":"CVE-2026-44429","sourceIdentifier":"security-advisories@github.com","published":"2026-05-14T21:16:46.677","lastModified":"2026-06-17T10:50:38.020","vulnStatus":"Analyzed","cveTags":[],"descriptions":[{"lang":"en","value":"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."}],"affected":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"modelcontextprotocol","product":"registry","versions":[{"version":"< 1.7.7","status":"affected"}]}]}],"metrics":{"cvssMetricV40":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"4.0","vectorString":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","baseScore":5.1,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"LOW","userInteraction":"PASSIVE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"LOW","subAvailabilityImpact":"LOW","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}],"cvssMetricV31":[{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N","baseScore":5.4,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"REQUIRED","scope":"CHANGED","confidentialityImpact":"LOW","integrityImpact":"LOW","availabilityImpact":"NONE"},"exploitabilityScore":2.3,"impactScore":2.7}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-05-15T14:19:51.887565Z","id":"CVE-2026-44429","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Secondary","description":[{"lang":"en","value":"CWE-79"},{"lang":"en","value":"CWE-116"}]}],"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:lfprojects:mcp_registry:*:*:*:*:*:*:*:*","versionEndExcluding":"1.7.7","matchCriteriaId":"158B1594-CF93-4F53-85DE-7909E8E4B136"}]}]}],"references":[{"url":"https://github.com/modelcontextprotocol/registry/security/advisories/GHSA-rqv2-m695-f8j4","source":"security-advisories@github.com","tags":["Exploit","Mitigation","Vendor Advisory"]},{"url":"https://github.com/modelcontextprotocol/registry/security/advisories/GHSA-rqv2-m695-f8j4","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","tags":["Exploit","Mitigation","Vendor Advisory"]}]}