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Permalink CVE-2026-44430
6.3 MEDIUM
  • CVSS version (CVSS): 4.0
  • Attack Vector (AV): Network (N)
  • Attack Complexity (AC): Low (L)
  • Attack Requirement (AT): Present (P)
  • Privileges Required (PR): None (N)
  • User Interaction (UI): None (N)
  • Vulnerable System Impact Confidentiality (VC): None (N)
  • Vulnerable System Impact Integrity (VI): None (N)
  • Vulnerable System Impact Availability (VA): None (N)
  • Subsequent System Impact Confidentiality (SC): Low (L)
  • Subsequent System Impact Integrity (SI): None (N)
  • Subsequent System Impact Availability (SA): None (N)
  • Modified Attack Vector (MAV): Network (N)
  • Modified Attack Complexity (MAC): Low (L)
  • Modified Attack Requirement (MAT): Present (P)
  • Modified Privileges Required (MPR): None (N)
  • Modified User Interaction (MUI): None (N)
  • Modified Vulnerable System Impact Confidentiality (MVC): None (N)
  • Modified Vulnerable System Impact Integrity (MVI): None (N)
  • Modified Vulnerable System Impact Availability (MVA): None (N)
  • Modified Subsequent System Impact Confidentiality (MSC): Low (L)
  • Modified Subsequent System Impact Integrity (MSI): Negligible (N)
  • Modified Subsequent System Impact Availability (MSA): Negligible (N)
  • Safety (S): Not Defined (X)
  • Automatable (AU): Not Defined (X)
  • Recovery (R): Not Defined (X)
  • Value Density (V): Not Defined (X)
  • Vulnerability Response Effort (RE): Not Defined (X)
  • Provider Urgency (U): Not Defined (X)
  • Confidentiality Req. (CR): Not Defined (X)
  • Integrity Req. (IR): Not Defined (X)
  • Availability Req. (AR): Not Defined (X)
  • Exploit Maturity (E): Not Defined (X)
updated 2 months, 1 week ago by @LeSuisse Activity log
  • Created suggestion 2 months, 1 week ago
  • @LeSuisse dismissed (not in Nixpkgs) 2 months, 1 week ago
MCP Registry: Unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, bypassing private-address allowlist

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 Registry's HTTP-based namespace verification (POST /v0/auth/http, POST /v0.1/auth/http) uses safeDialContext (internal/api/handlers/v0/auth/http.go:67-110) to refuse dialling private/internal addresses when fetching the well-known public-key file from a publisher-supplied domain. The blocklist (isBlockedIP, lines 125-133) relies entirely on Go stdlib's IsLoopback / IsPrivate / IsLinkLocalUnicast / IsMulticast / IsUnspecified plus a manual CGNAT range. None of these cover IPv6 6to4 (2002::/16), NAT64 (64:ff9b::/96 and 64:ff9b:1::/48 per RFC 8215), or deprecated site-local (fec0::/10) — all of which encode arbitrary IPv4 in the address bits and tunnel to RFC1918 / cloud-metadata services on dual-stack / NAT64-enabled hosts. This vulnerability is fixed in 1.7.7.

Affected products

registry
  • ==< 1.7.7

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