CVE-2026-55990
MEDIUM 5.9 ALL-YEARSIn NLnet Labs Unbound 1.7.0 up to and including 1.25.1, when the 'dnscrypt:' clause lists more 'dnscrypt-provider-cert:' files than there are matching 'dnscrypt-secret-key:' files, Unbound fills only the matched prefix and leaves the tail slots at the '0xdb' fill that libsodium's allocator writes into every allocation. Unbound would then iterate over the number of cert files, not the actual slots, so it walks into a slot with garbage data filled with '0xdb' bytes. Any unauthenticated client that sends one UDP datagram of ≥ 68 bytes whose first 8 bytes are '0xdb' to 'dnscrypt-port' will use that garbage entry which leads to a garbage dereference killing the server. This is a silent faulty configuration that goes unnoticed until triggered with the right client query. Unbound needs to be compiled with DNSCrypt support ('--enable-dnscrypt').
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.2%chance of exploitation in 30 days · 16th percentile
Impact if exploited
5.9CVSS 3.1 · MEDIUM · CNA
- ConfidentialityNone
- IntegrityNone
- AvailabilityHigh
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ✓Privileges: No account or privileges required
- ✓User interaction: No user interaction needed
- ⚠Complexity: Needs a race window or specific setup
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept
No public PoC is currently catalogued.
Search for new PoCs
Search GitHub now — results may be empty or unverified.
Tracked sources are checked weekly for the full archive, including PoCs published after the original disclosure. A later release appears after a tracked source lists it and a refresh succeeds.
Weakness (CWE)
- CWE-457: : Use of Uninitialized Variable
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
References and research data (JSON)
Vendor product assessments
Showing 32 of 35 vendor product statements; 3 omitted. Read the full vendor advisory.
unbound-main@aarch64 as a component of Red Hat Hardened Images · fixed
Vendor assessment for this product only.
pkg:rpm/redhat/[email protected]?arch=aarch64&distro=hummingbird-20251124&repository_id=public-hummingbird-aarch64-rpms
- vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/ Vendor guidance
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
unbound-main@noarch as a component of Red Hat Hardened Images · fixed
Vendor assessment for this product only.
pkg:rpm/redhat/[email protected]?arch=noarch&distro=hummingbird-20251124&repository_id=public-hummingbird-x86_64-rpms
- vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/ Vendor guidance
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
unbound-main@src as a component of Red Hat Hardened Images · fixed
Vendor assessment for this product only.
pkg:rpm/redhat/[email protected]?arch=src&distro=hummingbird-20251124&repository_id=public-hummingbird-source-rpms
- vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/ Vendor guidance
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
unbound-main@x86_64 as a component of Red Hat Hardened Images · fixed
Vendor assessment for this product only.
pkg:rpm/redhat/[email protected]?arch=x86_64&distro=hummingbird-20251124&repository_id=public-hummingbird-x86_64-rpms
- vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/ Vendor guidance
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
python3-unbound as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/python3-unbound
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound-anchor as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-anchor
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound-dracut as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-dracut
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound-libs as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-libs
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound-utils as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-utils
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound.src as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound?arch=src
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
python3-unbound as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/python3-unbound
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound-libs as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-libs
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound.src as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound?arch=src
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
python3-unbound as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/python3-unbound
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound-devel as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-devel
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound-dracut as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-dracut
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound.src as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound?arch=src
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
openshift/ose-rhel-coreos-8 as a component of Red Hat OpenShift Container Platform 4 · known affected
Vendor assessment for this product only.
pkg:oci/ose-rhel-coreos-8?repository_url=registry.redhat.io/openshift/ose-rhel-coreos-8
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
openshift/ose-rhel-coreos-9 as a component of Red Hat OpenShift Container Platform 4 · known affected
Vendor assessment for this product only.
pkg:oci/ose-rhel-coreos-9?repository_url=registry.redhat.io/openshift/ose-rhel-coreos-9
- workaround: To mitigate this issue, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.
- none available: Fix deferred
unbound as a component of Red Hat Enterprise Linux 6 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound-devel as a component of Red Hat Enterprise Linux 6 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound-devel
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound-libs as a component of Red Hat Enterprise Linux 6 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound-libs
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound-python as a component of Red Hat Enterprise Linux 6 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound-python
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound.src as a component of Red Hat Enterprise Linux 6 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound?arch=src
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound as a component of Red Hat Enterprise Linux 7 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound-devel as a component of Red Hat Enterprise Linux 7 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound-devel
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound-libs as a component of Red Hat Enterprise Linux 7 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound-libs
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound-python as a component of Red Hat Enterprise Linux 7 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound-python
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00unbound.src as a component of Red Hat Enterprise Linux 7 · known not affected
Vendor assessment for this product only.
Reason: vulnerable code not present
pkg:rpm/redhat/unbound?arch=src
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00
Known Affected Software Configurations
| Vendor | Product | Version range |
|---|---|---|
| Nlnetlabs | Unbound | ≥ 1.7.0 and < 1.25.2 |
All CVSS metrics
- MEDIUM 5.9 v3.1 · CNA Primary
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H - MEDIUM 5.9 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
References
Advisories
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55990.txt CVE record · NLnet Labs · Updated 2026-07-22T13:10:01.635Z
NVD · CVE-2026-55990 · Updated 2026-10-24T13:10:00.147
Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00 - https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-55990.json Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-47682 EUVD · EUVD-2026-47682
Technical & other
- https://access.redhat.com/security/cve/CVE-2026-55990 Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00
- https://bugzilla.redhat.com/show_bug.cgi?id=2506148 Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00
- https://www.cve.org/CVERecord?id=CVE-2026-55990 Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00
- https://nvd.nist.gov/vuln/detail/CVE-2026-55990 Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00
- https://access.redhat.com/errata/RHSA-2026:43588 Red Hat · CVE-2026-55990 · Updated 2026-09-01T12:38:25+00:00
Sources: NVD · CVE.org · All sources and attribution · EPSS