- Fix to ignore out-of-zone DNAME records for CNAME synthesis. Thanks

to Yuxiao Wu, Yiyi Wang, Zhang Chao, Baojun Liu, and Haixin Duan from
  Tsinghua University.

doc/Changelog

@@ -1,3 +1,8 @@
+13 March 2026: Yorgos
+	- Fix to ignore out-of-zone DNAME records for CNAME synthesis. Thanks
+	  to Yuxiao Wu, Yiyi Wang, Zhang Chao, Baojun Liu, and Haixin Duan from
+	  Tsinghua University.
+
 9 March 2026: Wouter
 	- Fix compile failure in unbound-checkconf for older gcc compiler.
 	- Merge #1418: Apply cache TTL policy to DNAME and synthesized

iterator/iter_scrub.c

@@ -466,8 +466,9 @@ scrub_normalize(sldns_buffer* pkt, struct msg_parse* msg,
 				pkt, msg, prev, &rrset);
 			continue;
 		}
-		if(rrset->type == LDNS_RR_TYPE_DNAME && 
-			pkt_strict_sub(pkt, sname, rrset->dname)) {
+		if(rrset->type == LDNS_RR_TYPE_DNAME &&
+			pkt_strict_sub(pkt, sname, rrset->dname) &&
+			pkt_sub(pkt, rrset->dname, zonename)) {
 			/* check if next rrset is correct CNAME. else,
 			 * synthesize a CNAME */
 			struct rrset_parse* nx = rrset->rrset_all_next;
@@ -534,7 +535,8 @@ scrub_normalize(sldns_buffer* pkt, struct msg_parse* msg,
 			if(nx && nx->section == LDNS_SECTION_ANSWER &&
 				nx->type == LDNS_RR_TYPE_DNAME &&
 				nx->rr_count == 1 &&
-				pkt_strict_sub(pkt, sname, nx->dname)) {
+				pkt_strict_sub(pkt, sname, nx->dname) &&
+				pkt_sub(pkt, nx->dname, zonename)) {
 				/* there is a DNAME after this CNAME, it 
 				 * is in the ANSWER section, and the DNAME
 				 * applies to the name we cover */

testdata/iter_scrub_dname_out_of_zone.rpl

@@ -0,0 +1,122 @@
+; config options
+server:
+	harden-referral-path: no
+	target-fetch-policy: "0 0 0 0 0"
+	qname-minimisation: "no"
+	minimal-responses: no
+	iter-scrub-promiscuous: no
+
+stub-zone:
+        name: "."
+	stub-addr: 193.0.14.129         # K.ROOT-SERVERS.NET.
+CONFIG_END
+
+SCENARIO_BEGIN Test scrub of out-of-zone DNAME in answer section
+
+STEP 10 QUERY
+ENTRY_BEGIN
+REPLY RD
+SECTION QUESTION
+x.y.example.com. IN A
+ENTRY_END
+
+; root prime is sent
+STEP 20 CHECK_OUT_QUERY
+ENTRY_BEGIN
+MATCH qname qtype opcode
+SECTION QUESTION
+. IN NS
+ENTRY_END
+STEP 30 REPLY
+ENTRY_BEGIN
+MATCH opcode qtype qname
+ADJUST copy_id
+REPLY QR AA NOERROR
+SECTION QUESTION
+. IN NS
+SECTION ANSWER
+. IN NS K.ROOT-SERVERS.NET.
+SECTION ADDITIONAL
+K.ROOT-SERVERS.NET. IN A 193.0.14.129
+ENTRY_END
+
+; query sent to root server
+STEP 40 CHECK_OUT_QUERY
+ENTRY_BEGIN
+MATCH qname qtype opcode
+SECTION QUESTION
+x.y.example.com. IN A
+ENTRY_END
+STEP 50 REPLY
+ENTRY_BEGIN
+MATCH opcode qtype qname
+ADJUST copy_id
+REPLY QR NOERROR
+SECTION QUESTION
+x.y.example.com. IN A
+SECTION AUTHORITY
+com. IN NS a.gtld-servers.net.
+SECTION ADDITIONAL
+a.gtld-servers.net. IN A 192.5.6.30
+ENTRY_END
+
+; query sent to .com server
+STEP 60 CHECK_OUT_QUERY
+ENTRY_BEGIN
+MATCH qname qtype opcode
+SECTION QUESTION
+x.y.example.com. IN A
+ENTRY_END
+
+STEP 70 REPLY
+ENTRY_BEGIN
+MATCH opcode qtype qname
+ADJUST copy_id
+REPLY QR NOERROR
+SECTION QUESTION
+x.y.example.com. IN A
+SECTION AUTHORITY
+example.com. IN NS ns1.example.com.
+SECTION ADDITIONAL
+ns1.example.com. IN A 168.192.2.2
+ENTRY_END
+
+STEP 80 CHECK_OUT_QUERY
+ENTRY_BEGIN
+MATCH qname qtype opcode
+SECTION QUESTION
+x.y.example.com. IN A
+ENTRY_END
+
+STEP 90 REPLY
+ENTRY_BEGIN
+MATCH opcode qtype qname
+ADJUST copy_id
+REPLY QR AA NOERROR
+SECTION QUESTION
+x.y.example.com. IN A
+SECTION ANSWER
+com. DNAME z.example.com.
+SECTION AUTHORITY
+example.com. IN NS ns1.example.com.
+SECTION ADDITIONAL
+ns1.example.com. IN A 168.192.2.2
+ENTRY_END
+
+; answer to first query
+; nodata answer since the DNAME is ignored for synthesis and scrubbed
+; all together.
+STEP 120 CHECK_ANSWER
+ENTRY_BEGIN
+MATCH all ttl
+REPLY QR RD RA
+SECTION QUESTION
+x.y.example.com. IN A
+SECTION ANSWER
+SECTION AUTHORITY
+example.com. IN NS ns1.example.com.
+SECTION ADDITIONAL
+ns1.example.com. IN A 168.192.2.2
+ENTRY_END
+
+SCENARIO_END