CVE-2026-85501
MEDIUM 5.3Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.5%chance of exploitation in 30 days · 41st percentile
Impact if exploited
5.3CVSS 3.1 · MEDIUM
- ConfidentialityNone
- IntegrityNone
- AvailabilityLow
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: No special conditions — reliably repeatable
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept
No public PoC is currently catalogued.
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Data snapshot:
Weakness (CWE)
- CWE-770: : Allocation of Resources Without Limits or Throttling
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References and research data (JSON)
Vendor product assessments
Showing 32 of 48 vendor product statements; 16 omitted. Read the full vendor advisory.
python3-unbound-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
python3-unbound-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-anchor-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-anchor-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-devel-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-dracut-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-dracut-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-libs-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-libs-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-munin-0:1.26.1-1.hum1@noarch@public-hummingbird-aarch64-rpms 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-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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-munin-0:1.26.1-1.hum1@noarch@public-hummingbird-x86_64-rpms 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-utils-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
unbound-utils-0:1.26.1-1.hum1@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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- none available: Fix deferred
unbound as a component of Red Hat Enterprise Linux 6 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound
- workaround: To mitigate implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- no fix planned: Out of support scope
unbound-libs as a component of Red Hat Enterprise Linux 6 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-libs
- workaround: To mitigate implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- no fix planned: Out of support scope
unbound.src as a component of Red Hat Enterprise Linux 6 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound?arch=src
- workaround: To mitigate implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- no fix planned: Out of support scope
unbound-devel as a component of Red Hat Enterprise Linux 7 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-devel
- workaround: To mitigate implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- none available: Fix deferred
unbound-python as a component of Red Hat Enterprise Linux 7 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-python
- workaround: To mitigate implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- none available: Fix deferred
unbound-devel as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/unbound-devel
- workaround: To mitigate implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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 implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- 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/[email protected]?repository_url=registry.redhat.io/openshift/ose-rhel-coreos-9
- workaround: To mitigate implement hard caps on iterative processing loops and resource allocations per request. Apply rate limiting and set strict connection/processing timeouts to prevent a single complex operation from tying up worker threads. For this specific flaw, administrators can also configure system-level resource constraints (like CPU cgroups) for the service.
- none available: Fix deferred
Known Affected Software Configurations
| Vendor | Product | Version range |
|---|---|---|
| Nlnetlabs | Unbound | < 1.26.1 |
All CVSS metrics
- MEDIUM 5.3 v3.1 · CNA Primary
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - MEDIUM 5.3 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - HIGH 7.5 v3.1 · NVD Primary
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
Patches & mitigations
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-85501.txt CVE record · NLnet Labs · Updated 2026-09-16T08:32:25.398Z
NVD · CVE-2026-85501 · Updated 2026-09-23T19:10:46.317
Red Hat · CVE-2026-85501 · Updated 2026-09-23T19:40:38+00:00
Advisories
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-85501.json Red Hat · CVE-2026-85501 · Updated 2026-09-23T19:40:38+00:00
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-80294 EUVD · EUVD-2026-80294
Technical & other
- https://access.redhat.com/security/cve/CVE-2026-85501 Red Hat · CVE-2026-85501 · Updated 2026-09-23T19:40:38+00:00
- https://bugzilla.redhat.com/show_bug.cgi?id=2535057 Red Hat · CVE-2026-85501 · Updated 2026-09-23T19:40:38+00:00
- https://www.cve.org/CVERecord?id=CVE-2026-85501 Red Hat · CVE-2026-85501 · Updated 2026-09-23T19:40:38+00:00
- https://nvd.nist.gov/vuln/detail/CVE-2026-85501 Red Hat · CVE-2026-85501 · Updated 2026-09-23T19:40:38+00:00
- https://access.redhat.com/errata/RHSA-2026:68590 Red Hat · CVE-2026-85501 · Updated 2026-09-23T19:40:38+00:00