Evidence used
- No CISA KEV confirmation is currently recorded.
- The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
- EPSS is 0.25% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-44621High confidence
Libunbound applications configured with 'unwanted-reply-threshold' could eventually be abruptly terminated
NLnet Labs · Unbound
5.9MediumCVSS 3.1
Patch only the product branches with a verified fix
Fix availability varies by productMedium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 30 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityMedium→Operational priority:Medium, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs NLnet Labs Unbound and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Remediation availability differs by product scope
Verified remediation exists for at least one product or source, but 30 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
- Red Hat Product Security: 29 affected or under-investigation product states without a fixed product state in the same current advisory
- Debian Security Tracker: 1 affected package state with no published fix
Distribution package intelligence
7 package statesRelease-specific package status
Alpine, Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
Package result overrides the generic status
BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 1 affected package state shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
| Distribution release | Source package | Vendor state | Fixed version | Evidence |
|---|---|---|---|---|
| Alpine v3.23v3.23 · main | unbound | Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected. | 1.25.2-r0 | Alpine Security Database ↗Source updated 3 Oct 2026 |
| Alpine v3.22v3.22 · main | unbound | Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected. | 1.25.2-r0 | Alpine Security Database ↗Source updated 3 Oct 2026 |
| Debian trixietrixie · source | unbound | Vendor fix publishedDebian records a fixed source-package version for this release. | 1.26.1-0+deb13u1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian bookwormbookworm · source | unbound | Affected, no fix publishedDebian currently tracks this release as open. | Not published in this feed | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian forkyforky · source | unbound | Vendor fix publishedDebian records a fixed source-package version for this release. | 1.25.2-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian sidsid · source | unbound | Vendor fix publishedDebian records a fixed source-package version for this release. | 1.25.2-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Ubuntu 24.04 LTSnoble · standard archive | unbound | Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing. | Not published in this feed | Canonical Ubuntu Security ↗Source updated 5 Oct 2026 |
Direct vendor intelligence
1 currentAuthoritative vendor CSAF and VEX advisories
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
CVE-2026-44621 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitylibunbound: libunbound: Denial of Service via specially crafted network traffic
The vendor explicitly identifies these products as affected by this CVE.
- python3-unbound as a component of Red Hat Enterprise Linux 10
- unbound as a component of Red Hat Enterprise Linux 10
- unbound-anchor as a component of Red Hat Enterprise Linux 10
- unbound-devel as a component of Red Hat Enterprise Linux 10
- unbound-dracut as a component of Red Hat Enterprise Linux 10
- unbound-libs as a component of Red Hat Enterprise Linux 10
- unbound-utils as a component of Red Hat Enterprise Linux 10
- unbound.src as a component of Red Hat Enterprise Linux 10
- unbound as a component of Red Hat Enterprise Linux 6
- unbound-devel as a component of Red Hat Enterprise Linux 6
- unbound-libs as a component of Red Hat Enterprise Linux 6
- unbound-python as a component of Red Hat Enterprise Linux 6
- Summary
- A flaw was found in libunbound, a library used by applications for DNS resolution. A remote attacker could exploit this vulnerability by sending specially crafted network traffic. This could cause applications using libunbound to terminate unexpectedly, leading to a denial of service (DoS). This occurs when the 'unwanted-reply-threshold' is configured, and the application attempts to call a cleanup function that is not properly allowed, resulting in a fatal exit.
- Remediation
- To mitigate this issue, ensure that any applications using `libunbound` do not set the `unwanted-reply-threshold` to a non-zero value. Disabling or setting this threshold to zero prevents the vulnerable code path from being triggered.
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 30 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Fix availability varies by product01
What, why and how
With NLnet Labs Unbound up to and including version 1.25.1, applications using libunbound and configured with 'unwanted-reply-threshold', could eventually be abruptly terminated if the threshold is reached and libunbound needs to call 'libworker_alloc_cleanup' since the function is absent from the function call allow list. When an application using libunbound sets 'unwanted-reply-threshold' to any non-zero value and the iterator queries an authoritative that replies with enough wrong-transaction-ID UDP datagrams to cross the threshold, the 'libworker_alloc_cleanup' will eventually be called. Since the function is absent from the function call allow list, this leads to a fatal exit of libunbound and eventual termination of the embedding application.Unbound itself is not affected since its relevant function 'worker_alloc_cleanup' is registed in the allow list and proceeds to perform the documented cache flush.
What
With NLnet Labs Unbound up to and including version 1.25.1, applications using libunbound and configured with 'unwanted-reply-threshold', could eventually be abruptly terminated if the threshold is reached and libunbound needs to call 'libworker_alloc_cleanup' since the function is absent from the function call allow list. When an application using libunbound sets 'unwanted-reply-threshold' to any non-zero value and the iterator queries an authoritative that replies with enough wrong-transaction-ID UDP datagrams to cross the threshold, the 'libworker_alloc_cleanup' will eventually be called. Since the function is absent from the function call allow list, this leads to a fatal exit of libunbound and eventual termination of the embedding application.Unbound itself is not affected since its relevant function 'worker_alloc_cleanup' is registed in the allow list and proceeds to perform the documented cache flush.
Why
The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
With NLnet Labs Unbound up to and including version 1.25.1, applications using libunbound and configured with 'unwanted-reply-threshold', could eventually be abruptly terminated if the threshold is reached and libunbound needs to call 'libworker_alloc_cleanup' since the function is absent from the function call allow list. When an application using libunbound sets 'unwanted-reply-threshold' to any non-zero value and the iterator queries an authoritative that replies with enough wrong-transaction-ID UDP datagrams to cross the threshold, the 'libworker_alloc_cleanup' will eventually be called. Since the function is absent from the function call allow list, this leads to a fatal exit of libunbound and eventual termination of the embedding application.Unbound itself is not affected since its relevant function 'worker_alloc_cleanup' is registed in the allow list and proceeds to perform the documented cache flush.
Why
The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
- Likely attack path
- a network path → Improper Check for Unusual or Exceptional Conditions → cause the confidentiality, integrity or availability impact described by the vendor
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- None
- Attack complexity
- High: exploitation depends on specific conditions
- Security boundary
- Unchanged: impact remains within the vulnerable component's security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-754 ↗
CWE-754: Improper Check for Unusual or Exceptional Conditions. The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:HCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.- Post-exploitation / living off the land
- No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Fix availability varies by product
- Affected
- python3-unbound as a component of Red Hat Enterprise Linux 10
- unbound as a component of Red Hat Enterprise Linux 10
- unbound-anchor as a component of Red Hat Enterprise Linux 10
- unbound-devel as a component of Red Hat Enterprise Linux 10
- unbound-dracut as a component of Red Hat Enterprise Linux 10
- unbound-libs as a component of Red Hat Enterprise Linux 10
- unbound-utils as a component of Red Hat Enterprise Linux 10
- unbound.src as a component of Red Hat Enterprise Linux 10
- unbound as a component of Red Hat Enterprise Linux 6
- unbound-devel as a component of Red Hat Enterprise Linux 6
- unbound-libs as a component of Red Hat Enterprise Linux 6
- unbound-python as a component of Red Hat Enterprise Linux 6
- unbound.src as a component of Red Hat Enterprise Linux 6
- unbound as a component of Red Hat Enterprise Linux 7
- unbound-devel as a component of Red Hat Enterprise Linux 7
- unbound-libs as a component of Red Hat Enterprise Linux 7
- unbound-python as a component of Red Hat Enterprise Linux 7
- unbound.src as a component of Red Hat Enterprise Linux 7
- python3-unbound as a component of Red Hat Enterprise Linux 8
- unbound as a component of Red Hat Enterprise Linux 8
- unbound-devel as a component of Red Hat Enterprise Linux 8
- unbound-libs as a component of Red Hat Enterprise Linux 8
- unbound.src as a component of Red Hat Enterprise Linux 8
- python3-unbound as a component of Red Hat Enterprise Linux 9
- unbound as a component of Red Hat Enterprise Linux 9
- unbound-devel as a component of Red Hat Enterprise Linux 9
- unbound-dracut as a component of Red Hat Enterprise Linux 9
- unbound-libs as a component of Red Hat Enterprise Linux 9
- unbound.src as a component of Red Hat Enterprise Linux 9
- Action
- Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
- Workaround
- To mitigate this issue, ensure that any applications using `libunbound` do not set the `unwanted-reply-threshold` to a non-zero value. Disabling or setting this threshold to zero prevents the vulnerable code path from being triggered.
04
Evidence and provenance
Published 22 Jul 2026 · Last source change 22 Jul 2026, 14:21 UTC · CWE-754 · Improper Check for Unusual or Exceptional Conditions
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-47667
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.