fix: prevent DNS rebinding bypass in SSRF protection (CWE-918)#186
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quangtran88 wants to merge 1 commit intoConway-Research:mainfrom
Open
fix: prevent DNS rebinding bypass in SSRF protection (CWE-918)#186quangtran88 wants to merge 1 commit intoConway-Research:mainfrom
quangtran88 wants to merge 1 commit intoConway-Research:mainfrom
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Add DNS resolution before IP blocklist check in fetchAgentCard to prevent attackers from using domains that resolve to private IPs. Also block IPv6-mapped IPv4 addresses (::ffff:x.x.x.x) and decimal IP notation in isInternalNetwork. Fail-closed on DNS resolution failure. Closes Conway-Research#183
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Summary
Prevent DNS rebinding attacks that bypass SSRF protection in agent card fetching. The previous implementation checked hostnames against a blocklist but didn't resolve DNS first — an attacker could register a domain resolving to
127.0.0.1and bypass the check.Changes
src/registry/discovery.ts:isInternalNetwork()— enhanced blocklist:::ffff:127.0.0.1→127.0.0.1)2130706433→127.0.0.1)resolveAndCheckHost()— new async DNS resolver:dns.lookup()before checking blocklistfetchAgentCard()— added DNS rebinding check:isAllowedUri()check, performs async DNS resolutionBackward Compatibility
isAllowedUri()remains synchronous — no API change for existing callersisInternalNetwork()signature unchanged — enhanced detection is additiveSecurity Impact
Before:
https://evil.attacker.com/card.jsonpasses SSRF check even ifevil.attacker.comresolves to127.0.0.1,10.0.0.1, etc.After: DNS is resolved and the actual IP is checked against the blocklist. Additionally blocks IPv6-mapped IPv4 and decimal IP evasion techniques.
Closes #183