Description
In NLnet Labs Unbound up to and including version 1.25.1, when 'unwanted-reply-threshold' is enabled (set to any value greater than zero), glue records of 0.0.0.0/::0 can short-circuit Unbound, on systems that can direct such traffic, by issuing DNS queries and receiving seemingly unwanted replies since the remote IP does not match the original source IP of 0.0.0.0/::0. This behavior keeps on looping for the glue records and pushing the counter to the configured 'unwanted-reply-threshold' that triggers a defensive cache clear. A malicious actor who controls a delegation that returns in-bailiwick glue of 0.0.0.0/::0 can drive the counter to the limit of 'unwanted-reply-threshold' to the threshold and trigger a cache clean of the message and rrset caches; at will, indefinitely, without sending a single spoofed packet. The iterator uses the 0.0.0.0/::0 glue, and a system that can route this (e.g., Linux kernel routes the datagram over loopback), Unbound's own listener answers from 127.0.0.1. Because of the mismatch of 0.0.0.0 and 127.0.0.1, in this example, Unbound accounts the reply as an unwanted (probably spoofed) answer. The counter resets to zero on every cache flush, so the attack loops forever.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| NLnet Labs | Unbound | < 1.25.2 | 1.25.2 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | unbound | 1.25.2-1 | — |
| Debian 13 | unbound | 1.26.1-0+deb13u1 | — |
| Debian 12 | unbound | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | unbound | No fix yet | — |
| Ubuntu 26.04 LTS | unbound | No fix yet | — |
| Ubuntu 24.04 LTS | unbound | No fix yet | — |
| Ubuntu 22.04 LTS | unbound | No fix yet | — |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | unbound | No fix yet | — |
| Ubuntu Pro 18.04 LTS | unbound | No fix yet | — |
| Ubuntu Pro 16.04 LTS | unbound | No fix yet | — |
| Ubuntu Pro 14.04 LTS | unbound | No fix yet | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | unbound +6 | 1.26.1-2.el10_3 | RHSA-2026:97121 |
| RHEL 9 | unbound +4 | 1.26.1-1.el9_9 | RHSA-2026:97497 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | unbound +7 | 1.25.2-0.1.hum1 | RHSA-2026:43588 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | unbound +6 | 1.26.1-2.el10_3 | RLSA-2026:97121 |
| Rocky Linux 9 | unbound +4 | 1.26.1-1.el9_9 | RLSA-2026:97497 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | unbound | 1.25.2-150600.23.19.1 | SUSE-SU-2026:3885-1 |
| SLES 15 SP6 | unbound | 1.25.2-150600.23.19.1 | SUSE-SU-2026:3885-1 |
| SLES 15 SP5 | unbound | 1.25.2-150100.10.28.1 | SUSE-SU-2026:3884-1 |
| SLES 15 SP4 | unbound | 1.25.2-150100.10.28.1 | SUSE-SU-2026:3884-1 |
Show 11 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | unbound | 1.25.2-160000.1.1 | SUSE-SU-2026:23226-1, SUSE-SU-2026:23215-1 |
| SLES for SAP 15 SP6 | unbound | 1.25.2-150600.23.19.1 | SUSE-SU-2026:3885-1 |
| SLES for SAP 15 SP5 | unbound | 1.25.2-150100.10.28.1 | SUSE-SU-2026:3884-1 |
| SLES for SAP 15 SP4 | unbound | 1.25.2-150100.10.28.1 | SUSE-SU-2026:3884-1 |
| SLES 16.0 | unbound | 1.25.2-160000.1.1 | SUSE-SU-2026:23226-1, SUSE-SU-2026:23215-1 |
| SLE Micro 6.2 | unbound | 1.25.2-160000.1.1 | SUSE-SU-2026:23050-1 |
| SLE Micro 6.1 | unbound | 1.25.2-slfo.1.1_1.1 | SUSE-SU-2026:23349-1 |
| SLE Micro 6.0 | unbound | 1.25.2-1.1 | SUSE-SU-2026:23360-1 |
| SLE Micro 5.5 | unbound | 1.25.2-150100.10.28.1 | SUSE-SU-2026:3884-1 |
| SLE HPC 15 SP5 | unbound | 1.25.2-150100.10.28.1 | SUSE-SU-2026:3884-1 |
| SLE HPC 15 SP4 | unbound | 1.25.2-150100.10.28.1 | SUSE-SU-2026:3884-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | unbound | 1.25.2-1.1 | openSUSE-SU-2026:11380-1 |
| openSUSE Leap 16.0 | unbound | 1.25.2-160000.1.1 | openSUSE-SU-2026:21550-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | unbound | 1.25.2-r0 | — |
| Alpine v3.23 | unbound | 1.25.2-r0 | — |
| Alpine v3.22 | unbound | 1.25.2-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | unbound +5 | 1.17.1-1.amzn2023.0.13 | ALAS2023-2026-2033 |
| Amazon Linux 2 | unbound +4 | 1.7.3-15.amzn2.0.15 | ALAS2-2026-3849 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | unbound | 1.25.2-1 | — |
Advisories 18
- RHSA-2026:97497 Red Hat Security Advisory: unbound security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:97121 Red Hat Security Advisory: unbound security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RLSA-2026:97497 Moderate: unbound security, bug fix, and enhancement update Rocky Linux Security Advisories · Nov 13, 2026
- RLSA-2026:97121 Moderate: unbound security, bug fix, and enhancement update Rocky Linux Security Advisories · Nov 13, 2026
- WID-SEC-2026-2492 Unbound: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 10, 2026
- RHSA-2026:43588 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- SUSE-SU-2026:3885-1 Security update for unbound SUSE / openSUSE Security Updates · Sep 10, 2026
- SUSE-SU-2026:3884-1 Security update for unbound SUSE / openSUSE Security Updates · Sep 10, 2026
- SUSE-SU-2026:23360-1 Security update for unbound SUSE / openSUSE Security Updates · Sep 10, 2026
- SUSE-SU-2026:23349-1 Security update for unbound SUSE / openSUSE Security Updates · Sep 10, 2026
- SUSE-SU-2026:23226-1 Security update for unbound SUSE / openSUSE Security Updates · Aug 27, 2026
- SUSE-SU-2026:23215-1 Security update for unbound SUSE / openSUSE Security Updates · Aug 27, 2026
- WID-SEC-2026-3038 Meinberg LANTIME: Mehrere Schwachstellen BSI CERT-Bund (WID) · Aug 26, 2026
- openSUSE-SU-2026:21550-1 Security update for unbound SUSE / openSUSE Security Updates · Aug 12, 2026
- SUSE-SU-2026:23050-1 Security update for unbound SUSE / openSUSE Security Updates · Aug 12, 2026
- ALAS2-2026-3849 Important: unbound security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Aug 4, 2026
- ALAS2023-2026-2033 Important: unbound security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 4, 2026
- openSUSE-SU-2026:11380-1 libunbound8-1.25.2-1.1 on GA media SUSE / openSUSE Security Updates · Jul 27, 2026
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50251.txt vendor-advisory