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OpenAdvisories
High · 7.5 CVE-2026-55973 EUVD-2026-47681GHSA-g479-fg97-pf5w

'dns-error-reporting: yes' leads to stack buffer overflow

Published Jul 22, 2026 · Updated Jul 22, 2026 · Assigned by NLnet Labs

Vendor: NLnet Labs Product: Unbound Package: unbound Package: unbound Package: unbound Package: unbound Ecosystem: Alpine Ecosystem: Azure Linux Ecosystem: Debian Ecosystem: Ubuntu

Description

In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.

Affected products

VendorProductAffectedFixed
NLnet Labs Unbound 1.23.0 – < 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 ↗
ReleasePackageFixed inAdvisory
Debian 14 unbound 1.25.2-1 —
Debian 13 unbound 1.26.1-0+deb13u1 —
Debian 12 unbound No fix yet —

Ubuntu

Security tracker ↗
ReleasePackageFixed inAdvisory
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)
ReleasePackageFixed inAdvisory
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 ↗
ReleasePackageFixed inAdvisory
RHEL 10 unbound +6 1.24.2-7.el10_2.4 RHSA-2026:55892
RHEL 9 unbound +4 1.24.2-3.el9_8.4 RHSA-2026:55841
Show 1 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
Red Hat Hardened Images 1 unbound +7 1.25.2-0.1.hum1 RHSA-2026:43588

AlmaLinux

Errata ↗
ReleasePackageFixed inAdvisory
AlmaLinux 10 unbound +6 1.24.2-7.el10_2.4 ALSA-2026:55892
AlmaLinux 9 unbound +4 1.24.2-3.el9_8.4 ALSA-2026:55841

Rocky Linux

Errata ↗
ReleasePackageFixed inAdvisory
Rocky Linux 10 unbound 1.24.2-7.el10_2.4 RLSA-2026:55892
Rocky Linux 9 unbound 1.24.2-3.el9_8.4 RLSA-2026:55841

SUSE

Security tracker ↗
ReleasePackageFixed inAdvisory
SLES for SAP 16.0 unbound 1.25.2-160000.1.1 SUSE-SU-2026:23226-1, SUSE-SU-2026:23215-1
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

openSUSE

Security tracker ↗
ReleasePackageFixed inAdvisory
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 ↗
ReleasePackageFixed inAdvisory
Alpine v3.24 unbound 1.25.2-r0 —
Alpine v3.23 unbound 1.25.2-r0 —
Alpine v3.22 unbound 1.25.2-r0 —

Azure Linux

ReleasePackageFixed inAdvisory
Azure Linux 3 unbound 1.25.2-1 —

Oracle Linux

ReleasePackageFixed inAdvisory
Oracle Linux 10 unbound +6 1.24.2-7.el10_2.4 ELSA-2026-55892
Oracle Linux 9 unbound +4 1.24.2-3.el9_8.4 ELSA-2026-55841

Advisories 18

References