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Full vulnerability report · 2026
CVE-2026-42944High confidence

Heap overflow with multiple NSID, COOKIE, PADDING EDNS options

NLnet Labs · Unbound

8.7HighCVSS 4.0
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

1 package state
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.

Ubuntu releaseSource packageVendor stateFixed versionEvidence
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 record ↗Source updated 9 Sept 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-2026-42944 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityunbound: Heap overflow and crash with multiple nsid, cookie, padding EDNS options
10 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • 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
Summary
A flaw was found in Unbound, a Domain Name System (DNS) resolver. A remote attacker could trigger a heap overflow by sending specially crafted DNS reply packets. This occurs when Unbound attempts to encode multiple Name Server Identifier (NSID) or Extension Mechanisms for DNS (EDNS) Cookie options, or EDNS Padding options, and these options are enabled. Successful exploitation of this vulnerability could lead to a denial of service (DoS), making the Unbound service unavailable.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Optional official sources

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

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

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-2026-31085

No EUVD known-exploited evidence

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

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
8.7 · CVSS 4.0
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

What

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

Why

Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.

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 vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

Why

Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.

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 → Numeric Truncation Error → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-197 ↗

CWE-197: Numeric Truncation Error. Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.

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:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Red

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.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATNoneAttack requirements: No additional deployment or execution condition is required.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-197
A

Official authority intelligence

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

ENISA EUVD · EUVD-2026-31085Official EUVD mapping

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

Official EUVD record
BSI · German · WID-SEC-W-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-W-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
CERT-FR · French · CERTFR-2026-AVI-0986Multiples vulnérabilités dans les produits IBM

d?id=CVE-2026-42496 Référence CVE CVE-2026-42497 https://www.cve.org/CVERecord?id=CVE-2026-42497 Référence CVE CVE-2026-42498 https://www.cve.org/CVERecord?id=CVE-2026-42498 Référence CVE CVE-2026-42580 https://www.cve.org/CVERecord?id=CVE-2026-42580 Référence CVE CVE-2026-42581 https://www.cve.org/CVERecord?id=CVE-2026-42581 Référence CVE CVE-2026-42583 https://www.cve.org/CVERecord?id=CVE-2026-42583 Référence CVE CVE-2026-42584 https://www.cve.org/CVERecord?id=CVE-2026-42584 Référence CVE CVE-2026-42585 https://www.cve.org/CVERecord?id=CVE-2026-42585 Référence CVE CVE-2026-42587 https://www.cve.org/CVERecord?id=CVE-2026-42587 Référence CVE CVE-2026-42944 https://www.cve.org/CVERecord?id=CVE-2026-42944 Référence CVE CVE-2026-42959 https://www.cve.org/CVERecord?id=CVE-2026-42959 Référence CVE CVE-2026-43020 https://www.cve.org/CVERecord?id=CVE-2026-43020 Référence CVE CVE-2026-43027 https://www.cve.org/CVERecord?id=CVE-2026-43027 Référence CVE CVE-2026-43037 https://www.cve.org/CVERecord?id=CVE-2026-43037 Référence CVE CVE-2026-43038 https://www.cve.org/CVERecord?id=CVE-2026-43038 Référence CVE CVE-2026-43051 https://www.cve.org/CVERecord?id=CVE-2026-43051 Référence CVE CVE-2026-43110 https://www.cve.org/CVERecord?id=CVE-2026-43110 Référence CVE CVE-2026-43125 https://www.cve.org/CVERecord?id=

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.
Patch available
Affected
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
Fixed
python3-unbound-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); python3-unbound-0:1.24.2-7.el10_2.1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10); python3-unbound-0:1.24.2-7.el10_2.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10); python3-unbound-0:1.24.2-7.el10_2.1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10); python3-unbound-debuginfo-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); python3-unbound-debuginfo-0:1.24.2-7.el10_2.1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10); python3-unbound-debuginfo-0:1.24.2-7.el10_2.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10); python3-unbound-debuginfo-0:1.24.2-7.el10_2.1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-0:1.24.2-7.el10_2.1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-0:1.24.2-7.el10_2.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-0:1.24.2-7.el10_2.1.src as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-0:1.24.2-7.el10_2.1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-0:1.24.2-7.el10_2.1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-0:1.24.2-7.el10_2.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-0:1.24.2-7.el10_2.1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-debuginfo-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-debuginfo-0:1.24.2-7.el10_2.1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-debuginfo-0:1.24.2-7.el10_2.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-anchor-debuginfo-0:1.24.2-7.el10_2.1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debuginfo-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debuginfo-0:1.24.2-7.el10_2.1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debuginfo-0:1.24.2-7.el10_2.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debuginfo-0:1.24.2-7.el10_2.1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debugsource-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debugsource-0:1.24.2-7.el10_2.1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debugsource-0:1.24.2-7.el10_2.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-debugsource-0:1.24.2-7.el10_2.1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10); unbound-dracut-0:1.24.2-7.el10_2.1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10); and 153 more
Action
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Workaround
A mitigation or workaround reference is available from the source linked below; validate it against the affected product and version.
04

Evidence and provenance

Published 20 May 2026 · Last source change 26 Aug 2026, 12:04 UTC · CWE-197 · Numeric Truncation Error

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-2026-31085
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Mitigation reference recorded
ENISA EUVD · EUVD-2026-31085↗Vendor CSAF · Red Hat Product Security↗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-2026-42944 · cve.blacktree.nl