From: Petr Špaček <pspacek@isc.org>
Date: Wed, 23 Jul 2025 15:25:18 +0000 (+0200)
Subject: Test that unsolicited NS in positive answer cannot overwrite current NS
X-Git-Tag: v9.21.17~14^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=658d2e9f8ec8408f227af034bd87cf4ff3189a88;p=thirdparty%2Fbind9.git

Test that unsolicited NS in positive answer cannot overwrite current NS

Before the fixes for CVE-2025-40778, an unsolicited in-bailiwick NS
record was accepted from a (spoofed) answer, enabling a single spoofed A
query/response to redirect traffic for a whole delegation.

In short, the attacker tries to spoof at least one answer that has the
following form:

    rcode NOERROR
    flags QR AA
    ;QUESTION
    trigger$RANDOM.victim. IN TXT
    ;ANSWER
    trigger$RANDOM.victim. 3600 IN TXT "spoofed answer with extra NS"
    ;AUTHORITY
    victim. 3600 IN NS ns.attacker.
    ;ADDITIONAL

This attack was originally reported as "test case 1".

Co-authored-by: Michał Kępień <michal@isc.org>
---

diff --git a/bin/tests/system/bailiwick/ans2/ans.py b/bin/tests/system/bailiwick/ans2/ans.py
index be072a39e16..d0ddccbe62d 100644
--- a/bin/tests/system/bailiwick/ans2/ans.py
+++ b/bin/tests/system/bailiwick/ans2/ans.py
@@ -29,6 +29,32 @@ ATTACKER_IP = "10.53.0.3"
 TTL = 3600
 
 
+class UnsolicitedNsSpoofer(ResponseSpoofer, mode="unsolicited-ns"):
+
+    qname = "trigger.victim."
+
+    async def get_responses(
+        self, qctx: QueryContext
+    ) -> AsyncGenerator[ResponseAction, None]:
+        response = qctx.prepare_new_response(with_zone_data=False)
+
+        txt_rrset = dns.rrset.from_text(
+            qctx.qname,
+            TTL,
+            qctx.qclass,
+            dns.rdatatype.TXT,
+            '"spoofed answer with extra NS"',
+        )
+        response.answer.append(txt_rrset)
+
+        ns_rrset = dns.rrset.from_text(
+            "victim.", TTL, qctx.qclass, dns.rdatatype.NS, "ns.attacker."
+        )
+        response.authority.append(ns_rrset)
+
+        yield DnsResponseSend(response, authoritative=True)
+
+
 def main() -> None:
     spoofing_server().run()
 
diff --git a/bin/tests/system/bailiwick/tests_bailiwick.py b/bin/tests/system/bailiwick/tests_bailiwick.py
index b068180265c..644fe5f24af 100644
--- a/bin/tests/system/bailiwick/tests_bailiwick.py
+++ b/bin/tests/system/bailiwick/tests_bailiwick.py
@@ -85,3 +85,12 @@ def test_bailiwick_sibling_ns_referral(servers: Dict[str, NamedInstance]) -> Non
     ns4 = servers["ns4"]
     send_trigger_query(ns4, "trigger.")
     check_domain_hijack(ns4)
+
+
+def test_bailiwick_unsolicited_authority(servers: Dict[str, NamedInstance]) -> None:
+    set_spoofing_mode(ans1="none", ans2="unsolicited-ns")
+
+    ns4 = servers["ns4"]
+    prime_cache(ns4)
+    send_trigger_query(ns4, "trigger.victim.")
+    check_domain_hijack(ns4)