EUVD-2026-67147
GHSA-8g5x-gj7x-mxgm
Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/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
DNS rebinding requires timing-dependent TTL expiry and browser behavior (AC:H); no server-side authentication needed (PR:N); victim must visit a malicious page (UI:R); no availability impact.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/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
Lifecycle Timeline
4DescriptionCVE.org
mcp-go accepted requests on its HTTP transports without checking the Host header. StreamableHTTPServer.ServeHTTP in server/streamable_http.go and SSEServer.ServeHTTP in server/sse.go served any request arriving over a loopback connection regardless of the host it named, and the SSE transport's cross-origin default allowed any origin. A page in a browser could therefore point a name it controlled at the loopback address and reach a server listening there, invoking tools and reading resources that the server exposed on the assumption that only local software could connect. No release before 0.56.0 validated the header on either transport; 0.56.0 adds server/http_localhost.go, which rejects a loopback-bound request carrying a host that is not a loopback name, and wires it into both transports.
AnalysisAI
DNS rebinding in mcp-go before 0.56.0 allows a malicious webpage to bypass localhost isolation and invoke tools or read resources on a victim's locally-running MCP server. Both StreamableHTTPServer and SSEServer accepted loopback connections without validating the Host header, and the SSE transport's permissive default CORS policy removed an additional browser-level barrier. …
Unlock full vulnerability intelligence
- Risk assessment & exploitation conditions
- Attack chain visualization
- Remediation with exact patch versions
- Threat intelligence from 22 sources
- Personal watchlist & email alerts
Free forever · No credit card required
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Two simultaneous conditions are required: the victim must be running an mcp-go server (version before 0.56.0) bound to a loopback address (127.0.0.1 or ::1), and the victim must visit an attacker-controlled web page in a browser. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 7.6 reflects AT:P (attack requirement: victim must be running mcp-go locally) and UI:P (victim must visit a malicious page), which meaningfully constrain real-world exploitation compared to fully automated network-vector attacks. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker registers a domain that briefly resolves to 127.0.0.1 through a DNS rebinding maneuver - exploiting short TTLs or DNS pinning bypasses - then serves a page that the victim developer visits while an mcp-go server is running locally. The page's JavaScript issues requests to the local MCP server with the attacker's domain as the Host header; without Host validation, the server accepts them, allowing the attacker's page to enumerate and invoke MCP tools (potentially reading local files, executing shell commands, or accessing credentials) entirely from within the browser. … |
| Remediation | Upgrade mcp-go to version 0.56.0 or later, which is the vendor-released patch confirming the fix. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, conduct an inventory of all systems running mcp-go versions prior to 0.56.0 and advise development teams to avoid accessing untrusted websites while MCP servers are active. …
Sign in for detailed remediation steps and compensating controls.
Threat intelligence, references, and detailed analysis are available after sign-in.
Same weakness CWE-346 – Origin Validation Error
View allSame technique Information Disclosure
View allShare
External POC / Exploit Code
Leaving vuln.today