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Full vulnerability report · 2026
CVE-2026-55990High confidence

Packet of death for a DNSCrypt misconfigured Unbound

NLnet Labs · Unbound

5.9MediumCVSS 3.1
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 0.36% 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.0Alpine 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.0Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourceunboundVendor fix publishedDebian records a fixed source-package version for this release.1.26.1-0+deb13u1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourceunboundAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourceunboundVendor fix publishedDebian records a fixed source-package version for this release.1.25.2-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourceunboundVendor fix publishedDebian records a fixed source-package version for this release.1.25.2-1Debian Security Tracker ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archiveunboundUnder evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical 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-2026-55990 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityunbound: NLnet Labs Unbound: Denial of Service via faulty DNSCrypt configuration
21 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
  • 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
Summary
A flaw was found in Unbound when configured with DNSCrypt support. An unauthenticated remote attacker could exploit a faulty configuration, where an imbalance between DNSCrypt provider certificate and secret key files leads to memory corruption. By sending a specially crafted network request, the attacker can cause a garbage dereference, leading to a server 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-2026-47682

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

In 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').

What

In 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').

Why

The code uses a variable that has not been initialized, leading to unpredictable or unintended results.

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

In 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').

Why

The code uses a variable that has not been initialized, leading to unpredictable or unintended results.

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
?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 → Use of Uninitialized Variable → 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-457 ↗

CWE-457: Use of Uninitialized Variable. The code uses a variable that has not been initialized, leading to unpredictable or unintended results.

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:H

Common 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.
NetworkUnauthenticatedCWE-457
A

Official authority intelligence

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

BSI · German · WID-SEC-2026-3038Meinberg LANTIME: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Meinberg LANTIME ausnutzen, um beliebigen Code auszuführen, Berechtigungen zu erweitern, Sicherheitsmaßnahmen zu umgehen, sensible Informationen offenzulegen, Daten zu manipulieren oder Denial-of-Service-Zustände herbeizuführen.

Official advisory ↗
BSI · German · WID-SEC-2026-2492Unbound: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Unbound ausnutzen, um einen Denial of Service Angriff durchzuführen, um Informationen offenzulegen, um Daten zu manipulieren, und um Sicherheitsvorkehrungen zu umgehen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260729Security Bulletin 29 Jul 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 29 Jul 2026, published on 29 July 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-025279NLnet Labsのunboundにおける初期化されていない変数の使用に関する脆弱性

NLnet Labs の Unbound バージョン 1.7.0 から 1.25.1 までにおいて、『dnscrypt:』句が『dnscrypt-secret-key:』ファイルの一致数より多くの『dnscrypt-provider-cert:』ファイルをリストしている場合、Unbound は一致したプレフィックスのみを埋め、残りのスロットは libsodium のアロケーターにより各割り当てに書き込まれる『0xdb』で満たされたままになります。Unbound は実際のスロット数ではなく、証明書ファイルの数に基づいて反復処理を行うため、『0xdb』バイトで埋められたガベージデータのスロットにアクセスしてしまいます。認証されていない任意のクライアントが、最初の 8 バイトが『0xdb』である長さ 68 バイト以上の UDP データグラムを『dnscrypt-port』に送信すると、そのガベージエントリを使用してガベージポインタ参照が発生し、サーバーがクラッシュします。これは正しいクライアントクエリでトリガーされるまで気付かれない静かな設定ミスです。Unbound は DNSCrypt サポート（『--enable-dnscrypt』）を有効にしてコンパイルする必要があります。

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 22 Jul 2026 · Last source change 22 Jul 2026, 14:04 UTC · CWE-457 · Use of Uninitialized Variable

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-2026-47682
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
    1.7.0 < 1.25.2 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    1.7.0 < 1.25.2 · 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 Awaiting fix to Patch available.
    Before
    Awaiting fix
    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; 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; 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; 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
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2026-47682↗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-2026-55990 · cve.blacktree.nl