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fix(security): block IPv6 transition addresses (NAT64/6to4/Teredo) in SSRF guard

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An attacker-controlled DNS record pointing at a NAT64 (64:ff9b::/96),
6to4 (2002::/16), or Teredo (2001:0000::/32) address that embeds a
private IPv4 (e.g. 64:ff9b::a9fe:a9fe = 169.254.169.254) bypassed the
SSRF guard: none of the guard functions recognised these ranges, so on a
host that routes the transition prefix the connection reached the
embedded private target (cloud metadata / internal SSRF).

Add a shared embeddedTransitionIpv4() detector and re-apply each guard's
own blocklist to the extracted IPv4 in isAlwaysBlocked, isPrivateNetwork,
isLinkLocal (ssrfGuard.ts) and isBlockedIp (egress-policy.ts). A
transition address to a public IPv4 stays allowed so legitimate
IPv6-only egress is unaffected.

egress-policy.ts keeps the detector inline to preserve its dependency-free
contract for the isolated plugin subprocess.
This commit is contained in:
jubnl
2026-07-18 17:16:47 +02:00
parent 3e61579347
commit c26a8e06f8
6 changed files with 209 additions and 0 deletions
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server/src/utils/ssrfGuard.ts
+12
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@@ -1,5 +1,6 @@
import dns from 'node:dns/promises';
import { Agent } from 'undici';
import { embeddedTransitionIpv4 } from './ipv6';
const ALLOW_INTERNAL_NETWORK = process.env.ALLOW_INTERNAL_NETWORK?.toLowerCase() === 'true';
@@ -23,6 +24,9 @@ function isAlwaysBlocked(ip: string): boolean {
if (addr.startsWith('169.254.') || /^fe80:/i.test(addr)) return true;
// IPv4-mapped loopback / link-local: ::ffff:127.x.x.x, ::ffff:169.254.x.x
if (/^::ffff:127\./i.test(addr) || /^::ffff:169\.254\./i.test(addr)) return true;
// IPv6 transition addresses (NAT64/6to4/Teredo) embedding a hard-blocked IPv4.
const embedded = embeddedTransitionIpv4(addr);
if (embedded) return isAlwaysBlocked(embedded);
return false;
}
@@ -43,6 +47,9 @@ function isPrivateNetwork(ip: string): boolean {
if (/^::ffff:10\./i.test(addr)) return true;
if (/^::ffff:172\.(1[6-9]|2\d|3[01])\./i.test(addr)) return true;
if (/^::ffff:192\.168\./i.test(addr)) return true;
// IPv6 transition addresses (NAT64/6to4/Teredo) embedding a private IPv4.
const embedded = embeddedTransitionIpv4(addr);
if (embedded) return isPrivateNetwork(embedded);
return false;
}
@@ -117,6 +124,11 @@ function isLinkLocal(ip: string): boolean {
// (100.64.0.0/10), which safeFetchLlm otherwise allows for a LAN model server —
// so block the specific metadata IPs directly rather than the whole range.
if (addr === '100.100.100.200' || addr === '100.100.100.100') return true;
// NAT64/6to4/Teredo embedding one of the above link-local/metadata IPs — extract
// the embedded IPv4 and re-check. A transition address to a public or LAN IPv4
// stays allowed (safeFetchLlm deliberately permits private/loopback targets).
const embedded = embeddedTransitionIpv4(addr);
if (embedded) return isLinkLocal(embedded);
return false;
}