Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.
History

Wed, 23 Sep 2026 19:30:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*

Thu, 17 Sep 2026 21:00:00 +0000

Type Values Removed Values Added
First Time appeared Nlnetlabs
Nlnetlabs unbound
Vendors & Products Nlnetlabs
Nlnetlabs unbound

Wed, 16 Sep 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 16 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Moderate


Wed, 16 Sep 2026 08:45:00 +0000

Type Values Removed Values Added
Description Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.
Title Retrap: Novel Vulnerabilities to launch Algorithmic Complexity Attacks on DNSSEC
Weaknesses CWE-770
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}


cve-icon MITRE

Status: PUBLISHED

Assigner: NLnet Labs

Published: 2026-09-16T08:32:25.398Z

Updated: 2026-09-16T14:12:18.996Z

Reserved: 2026-09-07T14:06:21.977Z

Link: CVE-2026-85501

cve-icon Vulnrichment

Updated: 2026-09-16T14:12:14.616Z

cve-icon NVD

Status : Analyzed

Published: 2026-09-16T09:17:06.783

Modified: 2026-09-23T19:10:46.317

Link: CVE-2026-85501

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-16T08:32:25Z

Links: CVE-2026-85501 - Bugzilla