Description
In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve as a secret value that increases the entropy of DNS transactions. When resolver load balancing policies depend on the source port while their outcome is revealed this secrecy is undermined. The vulnerability arises when the load balancing policy is consistent with respect to the incoming source UDP port and IP address while heavily depending on the incoming source UDP port as a randomization source. When the SO_REUSEPORT configuration option is enabled ('so-reuseport: yes') in Unbound (by default), it meets these conditions, making it vulnerable for DNS cache poisoning attacks. Upon startup, Unbound randomly partitions the available UDP source port space into disjoint subsets of (almost) equal size, assigning each subset to a specific worker thread. When an incoming DNS query is received, the kernel’s SO_REUSEPORT load balancing mechanism deterministically assigns the query to a socket associated with a particular thread. All outgoing DNS queries generated during the resolution of that request use source ports selected exclusively from the port subset assigned to the corresponding thread. Since these port subsets are disjoint across threads, the source port observed in a resolver’s outgoing query to an authoritative name server serves as a reliable indicator of the worker thread that processed the original client query. A malicious actor can acquire the mapping between incoming UDP source ports (for a given fixed source IP address) and Unbound worker threads and leverage it to conduct DNS cache poisoning attacks by effectively lowering the random port population per thread.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| NLnet Labs | Unbound | 1.4.22 – < 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 | 1.25.1-1ubuntu3.1 | USN-8946-2 |
| Ubuntu 26.04 LTS | unbound | 1.24.2-1ubuntu2.4 | USN-8946-1 |
| Ubuntu 24.04 LTS | unbound | 1.19.2-1ubuntu3.12 | USN-8946-1 |
| Ubuntu 22.04 LTS | unbound | 1.13.1-1ubuntu5.17 | USN-8946-1 |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | unbound | 1.9.4-2ubuntu1.11+esm3 | USN-8946-1 |
| Ubuntu Pro 18.04 LTS | unbound | 1.6.7-1ubuntu2.6+esm6 | USN-8946-1 |
| Ubuntu Pro 16.04 LTS | unbound | 1.5.8-1ubuntu1.1+esm5 | USN-8946-1 |
| Ubuntu Pro 14.04 LTS | unbound | 1.4.22-1ubuntu4.14.04.3+esm5 | USN-8946-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | unbound +6 | 1.24.2-7.el10_2.5 | RHSA-2026:68291 |
| RHEL 9 | unbound +4 | 1.24.2-3.el9_8.6 | RHSA-2026:68292 |
| RHEL 8 | unbound +3 | 1.16.2-5.14.el8_10.2 | RHSA-2026:69120 |
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 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 10 | unbound +6 | 1.24.2-7.el10_2.5 | ALSA-2026:68291 |
| AlmaLinux 9 | unbound +4 | 1.24.2-3.el9_8.6 | ALSA-2026:68292 |
| AlmaLinux 8 | unbound +3 | 1.16.2-5.14.el8_10.2 | ALSA-2026:69120 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | unbound | 1.24.2-7.el10_2.5 | RLSA-2026:68291 |
| Rocky Linux 9 | unbound | 1.24.2-3.el9_8.6 | RLSA-2026:68292 |
| Rocky Linux 8 | unbound | 1.16.2-5.14.el8_10.2 | RLSA-2026:69120 |
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 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | unbound | 1.25.2-1 | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 10 | unbound +6 | 1.24.2-7.el10_2.5 | ELSA-2026-68291 |
| Oracle Linux 9 | unbound +4 | 1.24.2-3.el9_8.6 | ELSA-2026-68292 |
| Oracle Linux 8 | unbound +3 | 1.16.2-5.14.el8_10.2 | ELSA-2026-69120 |
Advisories 27
- USN-8946-2 unbound vulnerabilities Ubuntu Security Notices (USN) · Nov 11, 2026
- WID-SEC-2026-2492 Unbound: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 10, 2026
- ALSA-2026:68292 Moderate: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:68291 Moderate: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:69120 Moderate: unbound security update AlmaLinux Security Advisories · Oct 29, 2026
- USN-8946-1 unbound vulnerabilities Ubuntu Security Notices (USN) · Oct 21, 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
- RHSA-2026:69120 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:68292 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- RHSA-2026:68291 Red Hat Security Advisory: unbound security update Red Hat Security Advisories (RHSA) · Oct 19, 2026
- ELSA-2026-69120 Moderate: unbound security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Sep 23, 2026
- RLSA-2026:69120 Moderate: unbound security update Rocky Linux Security Advisories · Sep 22, 2026
- RLSA-2026:68291 Moderate: unbound security update Rocky Linux Security Advisories · Sep 17, 2026
- RLSA-2026:68292 Moderate: unbound security update Rocky Linux Security Advisories · Sep 17, 2026
- ELSA-2026-68291 Moderate: unbound security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Sep 17, 2026
- ELSA-2026-68292 Moderate: unbound security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Sep 16, 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-2026:23349-1 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-2026:23226-1 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
- 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-2026-50252.txt vendor-advisory