Improper Initialization in Unbound - CVE-2026-55990

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Main Vulnerability Database Vulnerabilities #VU139221

Improper Initialization in Unbound - CVE-2026-55990

Published: July 23, 2026


Vulnerability identifier: #VU139221
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-55990
CWE-ID: CWE-665
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to improper initialization in the DNSCrypt certificate array handling in Unbound when processing a UDP datagram sent to dnscrypt-port under a faulty DNSCrypt configuration with more certificate files than matching secret key files. A remote attacker can send a specially crafted UDP datagram whose first 8 bytes are 0xdb to cause a denial of service.

Only installations compiled with DNSCrypt support are affected, and exploitation requires a silent faulty configuration in which the number of dnscrypt-provider-cert files exceeds the number of matching dnscrypt-secret-key files.


Affected software

Unbound
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Micro
SUSE Package Hub 15
Basesystem Module
openSUSE Leap
openEuler
Anolis OS
Fedora
unbound
python3-unbound
unbound-debuginfo
unbound-debugsource
unbound-devel
unbound-help
unbound-libs
unbound-anchor
unbound-utils
libunbound8
libunbound8-debuginfo
unbound-anchor-debuginfo
unbound-munin
unbound-python
unbound-python-debuginfo
libunbound-devel-mini-debuginfo
libunbound-devel-mini-debugsource
libunbound-devel-mini

How to mitigate CVE-2026-55990

Install security update from vendor's website.

Unbound - update to 1.25.2
unbound - addressed in versions 1.11.0-25, 1.13.2-25, 1.17.1-19, 1.17.1-20
python3-unbound - addressed in versions 1.11.0-25, 1.13.2-25, 1.17.1-19, 1.17.1-20
unbound-debuginfo - addressed in versions 1.11.0-25, 1.13.2-25, 1.17.1-19, 1.17.1-20
unbound-debugsource - addressed in versions 1.11.0-25, 1.13.2-25, 1.17.1-19, 1.17.1-20
unbound-devel - addressed in versions 1.11.0-25, 1.13.2-25, 1.17.1-19, 1.17.1-20
unbound-help - addressed in versions 1.11.0-25, 1.13.2-25, 1.17.1-19, 1.17.1-20
unbound-libs - addressed in versions 1.11.0-25, 1.13.2-25, 1.17.1-19, 1.17.1-20
unbound-anchor - addressed in versions 1.13.2-25, 1.17.1-19, 1.17.1-20
python3-unbound - update to 1.17.1-14
unbound - update to 1.17.1-14
unbound-anchor - update to 1.17.1-14
unbound-devel - update to 1.17.1-14
unbound-libs - update to 1.17.1-14
unbound-utils - update to 1.17.1-14
unbound-utils - addressed in versions 1.17.1-19, 1.17.1-20
unbound - update to 1.25.2-1.fc43
libunbound8 - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-devel - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
libunbound8-debuginfo - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-anchor - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-debugsource - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-anchor-debuginfo - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-debuginfo - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-munin - update to 1.25.2-150600.23.19.1
unbound-python - update to 1.25.2-150600.23.19.1
unbound - update to 1.25.2-150600.23.19.1
unbound-python-debuginfo - update to 1.25.2-150600.23.19.1
libunbound-devel-mini-debuginfo - update to 1.25.2-150600.23.19.1
libunbound-devel-mini-debugsource - update to 1.25.2-150600.23.19.1
libunbound-devel-mini - update to 1.25.2-150600.23.19.1

External References

Related Security Bulletins