commit c3d4f3da3d34f5c82d179e4f2b9fd7c12243000f Author: Jorik Cronenberg Date: Wed Apr 1 13:09:21 2026 +0200 [9.18] [CVE-2026-1519] sec: usr: Fix unbounded NSEC3 iterations when validating referrals to unsigned delegations diff --git a/lib/dns/include/dns/types.h b/lib/dns/include/dns/types.h index 6465962bd4..1e060ef918 100644 --- a/lib/dns/include/dns/types.h +++ b/lib/dns/include/dns/types.h @@ -351,6 +351,7 @@ enum { ((x) == dns_trust_additional || (x) == dns_trust_pending_additional) #define DNS_TRUST_GLUE(x) ((x) == dns_trust_glue) #define DNS_TRUST_ANSWER(x) ((x) == dns_trust_answer) +#define DNS_TRUST_SECURE(x) ((x) >= dns_trust_secure) /*% * Name checking severities. diff --git a/lib/dns/validator.c b/lib/dns/validator.c index 582058b3a7..02e5d2a174 100644 --- a/lib/dns/validator.c +++ b/lib/dns/validator.c @@ -252,12 +252,25 @@ exit_check(dns_validator_t *val) { } /*% - * Look in the NSEC record returned from a DS query to see if there is - * a NS RRset at this name. If it is found we are at a delegation point. + * The isdelegation() function is called as part of seeking the DS record. + * Look in the NSEC or NSEC3 record returned from a DS query to see if the + * record has the NS bitmap set. If so, we are at a delegation point. + * + * If the response contains NSEC3 records with too high iterations, we cannot + * (or rather we are not going to) validate the insecurity proof. Instead we + * are going to treat the message as insecure and just assume the DS was at + * the delegation. + * + * Returns: + *\li #ISC_R_SUCCESS the NS bitmap was set in the NSEC or NSEC3 record, or + * the NSEC3 covers the name (in case of opt-out), or + * we cannot validate the insecurity proof and are going + * to treat the message as isnecure. + *\li #ISC_R_NOTFOUND the NS bitmap was not set, */ -static bool -isdelegation(dns_name_t *name, dns_rdataset_t *rdataset, - isc_result_t dbresult) { +static isc_result_t +isdelegation(dns_validator_t *val, dns_name_t *name, dns_rdataset_t *rdataset, + isc_result_t dbresult, const char *caller) { dns_fixedname_t fixed; dns_label_t hashlabel; dns_name_t nsec3name; @@ -285,7 +298,7 @@ isdelegation(dns_name_t *name, dns_rdataset_t *rdataset, goto trynsec3; } if (result != ISC_R_SUCCESS) { - return false; + return ISC_R_NOTFOUND; } } @@ -299,7 +312,7 @@ isdelegation(dns_name_t *name, dns_rdataset_t *rdataset, dns_rdata_reset(&rdata); } dns_rdataset_disassociate(&set); - return found; + return found ? ISC_R_SUCCESS : ISC_R_NOTFOUND; trynsec3: /* @@ -335,6 +348,18 @@ trynsec3: if (nsec3.hash != 1) { continue; } + /* + * If there are too many iterations assume bad things + * are happening and bail out early. Treat as if the + * DS was at the delegation. + */ + if (nsec3.iterations > DNS_NSEC3_MAXITERATIONS) { + validator_log(val, ISC_LOG_DEBUG(3), + "%s: too many iterations", + caller); + dns_rdataset_disassociate(&set); + return ISC_R_SUCCESS; + } length = isc_iterated_hash( hash, nsec3.hash, nsec3.iterations, nsec3.salt, nsec3.salt_length, name->ndata, name->length); @@ -346,7 +371,7 @@ trynsec3: found = dns_nsec3_typepresent(&rdata, dns_rdatatype_ns); dns_rdataset_disassociate(&set); - return found; + return found ? ISC_R_SUCCESS : ISC_R_NOTFOUND; } if ((nsec3.flags & DNS_NSEC3FLAG_OPTOUT) == 0) { continue; @@ -362,12 +387,12 @@ trynsec3: memcmp(hash, nsec3.next, length) < 0))) { dns_rdataset_disassociate(&set); - return true; + return ISC_R_SUCCESS; } } dns_rdataset_disassociate(&set); } - return found; + return found ? ISC_R_SUCCESS : ISC_R_NOTFOUND; } /*% @@ -583,8 +608,9 @@ fetch_callback_ds(isc_task_t *task, isc_event_t *event) { } else if (eresult == DNS_R_SERVFAIL) { goto unexpected; } else if (eresult != DNS_R_CNAME && - isdelegation(devent->foundname, &val->frdataset, - eresult)) + isdelegation(val, devent->foundname, &val->frdataset, + eresult, + "fetch_callback_ds") == ISC_R_SUCCESS) { /* * Failed to find a DS while trying to prove @@ -744,10 +770,13 @@ validator_callback_ds(isc_task_t *task, isc_event_t *event) { dns_trust_totext(val->frdataset.trust)); have_dsset = (val->frdataset.type == dns_rdatatype_ds); name = dns_fixedname_name(&val->fname); + if ((val->attributes & VALATTR_INSECURITY) != 0 && val->frdataset.covers == dns_rdatatype_ds && NEGATIVE(&val->frdataset) && - isdelegation(name, &val->frdataset, DNS_R_NCACHENXRRSET)) + isdelegation(val, name, &val->frdataset, + DNS_R_NCACHENXRRSET, + "validator_callback_ds") == ISC_R_SUCCESS) { result = markanswer(val, "validator_callback_ds", "no DS and this is a delegation"); @@ -1471,6 +1500,13 @@ verify(dns_validator_t *val, dst_key_t *key, dns_rdata_t *rdata, bool ignore = false; dns_name_t *wild; + if (DNS_TRUST_SECURE(val->event->rdataset->trust)) { + /* + * This RRset was already verified before. + */ + return ISC_R_SUCCESS; + } + val->attributes |= VALATTR_TRIEDVERIFY; wild = dns_fixedname_initname(&fixed); again: @@ -2411,6 +2447,17 @@ validate_neg_rrset(dns_validator_t *val, dns_name_t *name, } } + if (rdataset->type != dns_rdatatype_nsec && + DNS_TRUST_SECURE(rdataset->trust)) + { + /* + * The negative response data is already verified. + * We skip NSEC records, because they require special + * processing in validator_callback_nsec(). + */ + return DNS_R_CONTINUE; + } + val->currentset = rdataset; result = create_validator(val, name, rdataset->type, rdataset, sigrdataset, validator_callback_nsec, @@ -2521,11 +2568,9 @@ validate_ncache(dns_validator_t *val, bool resume) { } result = validate_neg_rrset(val, name, rdataset, sigrdataset); - if (result == DNS_R_CONTINUE) { - continue; + if (result != DNS_R_CONTINUE) { + return result; } - - return result; } if (result == ISC_R_NOMORE) { result = ISC_R_SUCCESS; @@ -2574,7 +2619,8 @@ validate_nx(dns_validator_t *val, bool resume) { result = findnsec3proofs(val); if (result == DNS_R_NSEC3ITERRANGE) { validator_log(val, ISC_LOG_DEBUG(3), - "too many iterations"); + "%s: too many iterations", + __func__); markanswer(val, "validate_nx (3)", NULL); return ISC_R_SUCCESS; } @@ -2610,7 +2656,7 @@ validate_nx(dns_validator_t *val, bool resume) { result = findnsec3proofs(val); if (result == DNS_R_NSEC3ITERRANGE) { validator_log(val, ISC_LOG_DEBUG(3), - "too many iterations"); + "%s: too many iterations", __func__); markanswer(val, "validate_nx (4)", NULL); return ISC_R_SUCCESS; } @@ -2827,8 +2873,10 @@ seek_ds(dns_validator_t *val, isc_result_t *resp) { return ISC_R_COMPLETE; } - if (isdelegation(tname, &val->frdataset, result)) { - *resp = markanswer(val, "proveunsecure (4)", + result = isdelegation(val, tname, &val->frdataset, result, + "seek_ds"); + if (result == ISC_R_SUCCESS) { + *resp = markanswer(val, "seek_ds (3)", "this is a delegation"); return ISC_R_COMPLETE; }