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Full vulnerability report · 2026
CVE-2026-44608High confidence

Use after free and crash under special conditions in RPZ code

NLnet Labs · Unbound

4.6MediumCVSS 4.0
Recommended action
Patch only the product branches with a verified fix

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 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Medium, unchanged from published severity.unchanged

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 0.28% for the current model date.

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

  1. Confirm that the asset runs NLnet Labs Unbound and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-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.

7 package states
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 releaseSource packageVendor stateFixed versionEvidence
Alpine v3.23v3.23 · mainunboundVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.25.2-r0Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.22v3.22 · mainunboundVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.25.2-r0Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourceunboundVendor fix publishedDebian records a fixed source-package version for this release.1.22.0-2+deb13u3Debian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourceunboundAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourceunboundVendor fix publishedDebian records a fixed source-package version for this release.1.25.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourceunboundVendor fix publishedDebian records a fixed source-package version for this release.1.25.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Ubuntu 24.04 LTSnoble · standard archiveunboundVendor fix publishedCanonical reports that a fixed source package version has been published. Repository candidate availability is not checked by BlackTree.1.19.2-1ubuntu3.8Canonical Ubuntu Security ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative 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.

1 current
CVE-2026-44608 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityunbound: Unbound: Denial of Service due to locking inconsistency during RPZ XFR reload
31 known affected

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 Unbound. When operating in a multi-threaded configuration with specific Response Policy Zones (RPZ) using 'rpz-nsip' or 'rpz-nsdname' triggers, a locking inconsistency during an RPZ zone transfer (XFR) reload can occur. This timing issue may allow an adversary to trigger a heap use-after-free vulnerability, leading to a system crash and a Denial of Service (DoS).
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-31087

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

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 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.

What

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.

Why

The product does not lock or does not correctly lock a resource when the product must have exclusive access to the resource.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.

Why

The product does not lock or does not correctly lock a resource when the product must have exclusive access to the resource.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

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
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

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 Resource Locking → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-413 ↗

CWE-413: Improper Resource Locking. The product does not lock or does not correctly lock a resource when the product must have exclusive access to the resource.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber

Common Vulnerability Scoring System 4.0: 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.ATPresentAttack requirements: A particular deployment or execution condition must be present.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VINoneVulnerable-system integrity: No direct loss is represented by this metric.VAHighVulnerable-system availability: A successful attack can cause a major loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
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.
NetworkUnauthenticatedDenial of serviceCWE-413
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-2455Oracle Solaris Drittanbieterkomponenten: Mehrere Schwachstellen

Ein entfernter, anonymer oder authentisierter Angreifer kann mehrere Schwachstellen in verschiedenen Komponenten von Drittanbietern in Oracle Solaris ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.

Official advisory ↗
BSI · German · WID-SEC-2026-1599Unbound: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Unbound ausnutzen, um einen Denial of Service Zustand herbeizuführen, um möglicherweise Code auszuführen und um nicht näher spezifizierte Auswirkungen zu verursachen.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-016790NLnet Labsのunboundにおける不適切なリソースロックに関する脆弱性

NLnet LabsのUnboundバージョン1.14.0から1.25.0まで（1.25.0を含む）には、特定の条件が満たされた場合（マルチスレッド、RPZ XFRリロード、'rpz-nsip'または'rpz-nsdname'トリガーを持つRPZゾーン）にヒープのuse-after-freeおよび最終的なクラッシュを引き起こすロックの不整合の脆弱性が存在します。攻撃者は、脆弱なUnboundがマルチスレッドで動作し、'rpz-nsip'または'rpz-nsdname'トリガーを持つRPZゾーンがあり、そのRPZゾーンのXFRが進行中である場合に限り、この脆弱性を悪用可能です。ローカルRPZファイルではこの脆弱性は発生しません。タイミングが合い、XFRの実行中に別のスレッドが同じRPZゾーンを読み込もうとすると、リーダーがロックを保持する時間が十分でない可能性があり、XFRを適用するスレッドがリーダーがアクセスしようとしているオブジェクトを解放するため、use-after-freeが発生します。Unbound 1.25.1には、このロックコードの修正パッチが含まれています。

Official advisory ↗
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
Fixed
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
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 20 May 2026 · Last source change 20 May 2026, 12:54 UTC · CWE-413 · Improper Resource Locking

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-31087
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

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    1.14.0 < 1.25.1 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    1.14.0 < 1.25.1 · Fixed: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
    Red Hat Product Security ↗
  2. Remediation statusRemediation status changed from Mitigation available to Patch available.
    Before
    Mitigation available
    After
    Patch available
    Red Hat Product Security ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    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; openshift/ose-rhel-coreos-9 as a component of Red Hat OpenShift Container Platform 4 · Fixed: unbound-main@aarch64 as a component of Red Hat Hardened Images; unbound-main@noarch as a component of Red Hat Hardened Images; unbound-main@src as a component of Red Hat Hardened Images; unbound-main@x86_64 as a component of Red Hat Hardened Images
    After
    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; openshift/ose-rhel-coreos-8 as a component of Red Hat OpenShift Container Platform 4; and 1 more · Fixed: unbound-main@aarch64 as a component of Red Hat Hardened Images; unbound-main@noarch as a component of Red Hat Hardened Images; unbound-main@src as a component of Red Hat Hardened Images; unbound-main@x86_64 as a component of Red Hat Hardened Images
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Mitigation reference recorded
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2026-31087↗Red Hat Product Security security advisory↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
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.
Free version - for non-commercial use only.CVE-2026-44608 · cve.blacktree.nl