# CVE-2026-85501: Retrap: Novel Vulnerabilities to launch Algorithmic Complexity Attacks on DNSSEC CVE-2026-85501 is fixed in 16 products on 1 platform, first by libunbound2 1.6.7-1ubuntu2.6+esm6, released September 16, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-85501 - Priority: High - CVSS: 7.5 (Moderate) - EPSS: 0.0048 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Sep 16, 2026 - Weakness: Allocation of Resources Without Limits or Throttling - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-85501 ## 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. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | libunbound2 Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [libunbound2 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libunbound2-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [libunbound8 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libunbound8-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [libunbound8 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libunbound8-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [libunbound8 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libunbound8-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [libunbound8 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libunbound8-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | python-unbound Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [python-unbound 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-python-unbound-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | python-unbound Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [python-unbound 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-python-unbound-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [python3-unbound 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-python3-unbound-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [python3-unbound 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-python3-unbound-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [python3-unbound 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-python3-unbound-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [python3-unbound 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-python3-unbound-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [python3-unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-python3-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | python3-unbound amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | python3-unbound-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-85501](https://patchblox.com/security/data/fix/linux/debian-cve-2026-85501.md) | Sep 19, 2026 | | Linux | unbound Debian 14 | 1.26.1-1 | [DEBIAN-CVE-2026-85501](https://patchblox.com/security/data/fix/linux/debian-cve-2026-85501.md) | Sep 19, 2026 | | Linux | unbound Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [unbound 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-unbound-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [unbound 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-unbound-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [unbound 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-unbound-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [unbound 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-unbound-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound opensuse-leap 16.0 | 1.26.1-160000.1.1 | [OPENSUSE-SU-2026:22082-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-22082-1.md) | Nov 7, 2026 | | Linux | unbound sles 15.6 | 1.26.1-150600.23.24.1 | [SUSE-SU-2026:4620-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-4620-1.md) | Nov 7, 2026 | | Linux | unbound sles 15.7 | 1.26.1-150600.23.24.1 | [SUSE-SU-2026:4620-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-4620-1.md) | Nov 7, 2026 | | Linux | unbound sles 16.0 | 1.26.1-160000.1.1 | [SUSE-SU-2026:24226-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-24226-1.md) | Nov 7, 2026 | | Linux | unbound-anchor Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [unbound-anchor 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-unbound-anchor-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [unbound-anchor 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-unbound-anchor-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [unbound-anchor 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-unbound-anchor-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [unbound-anchor 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-unbound-anchor-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-anchor 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-anchor-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound-anchor amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-anchor-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-debugsource amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-devel amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-host Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [unbound-host 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-unbound-host-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [unbound-host 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-unbound-host-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [unbound-host 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-unbound-host-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [unbound-host 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-unbound-host-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-host 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-host-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound-libs amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-libs-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-utils amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | | Linux | unbound-utils-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.15 | [ALAS2023-2026-3127](https://patchblox.com/security/data/fix/linux/alas2023-2026-3127.md) | Sep 28, 2026 | --- Data as of 2026-11-08T00:53:09Z UTC. 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