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Full vulnerability report · 2026
CVE-2026-82399High confidence

CoreDNS: Unauthenticated memory exhaustion in custom transports

coredns · coredns

Official source article: GitHub GHSA-MRG3-QVQR-JW29 ↗. Check the applicable product and release in the original source.

7.5HighCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 3 structured product or package states 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 severityHighOperational priority:Critical, raised one band.upgradedsince 18 Sep 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • A structured source references public exploit or proof-of-concept material.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 0.61% 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.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs coredns coredns 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: Within 3 daysRemediation target: Within 90 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 3 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Open-source package ranges3 source-attributed ranges

These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.

Ecosystem and packageAffected rangeFirst fixed versionEvidence
Gogithub.com/coredns/corednsSEMVER: introduced 0; fixed 1.14.71.14.7OSV record ↗aggregator derived · 28 Sep 2026
Gogithub.com/coredns/corednsSEMVER: introduced 0; fixed 1.14.71.14.7OSV record ↗aggregator derived · 28 Sep 2026
gogithub.com/coredns/coredns<= 1.14.61.14.7GitHub advisory ↗upstream repository advisory · 17 Sep 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-2026-82399 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitygithub.com/coredns/coredns: CoreDNS: Denial of Service due to unauthenticated memory exhaustion in custom transports
3 known affected

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

  • rhcl-1/coredns-rhel9 as a component of Red Hat Connectivity Link 1
  • openshift4/ose-coredns as a component of Red Hat OpenShift Container Platform 4
  • openshift4/ose-coredns-rhel9 as a component of Red Hat OpenShift Container Platform 4
Summary
A flaw was found in CoreDNS. An unauthenticated remote attacker can exploit this vulnerability by sending specially crafted DNS requests over custom transports, such as DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC. By using DNS name compression and excessive section counts, the attacker can cause the server to exhaust its memory, leading to a Denial of Service (DoS) where CoreDNS terminates. The ordinary UDP and TCP listeners are not affected.
Remediation
There is no complete mitigation available for this issue without upgrading. However, administrators can reduce risk by implementing the following interim measures: 1. If DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, or DNS-over-gRPC are not required, disable these custom transport protocols and use only standard UDP/TCP DNS, which is not affected by this vulnerability. 2. Implement network-level rate limiting for HTTPS and QUIC traffic to CoreDNS endpoints to reduce the effectiveness of concurrent memory exhaustion attacks. 3. Configure resource limits (memory limits) for CoreDNS pods to prevent a single CoreDNS instance from consuming all node memory, and ensure sufficient pod replicas for high availability. 4. Monitor CoreDNS memory usage and configure alerts for unusual memory consumption patterns or Out-of-Memory events. 5. Restrict network access to CoreDNS custom transport endpoints to trusted clients only using NetworkPolicies or firewall rules. Apply updates as they become available from Red Hat product teams. For OpenShift clusters, prioritize patching environments where DNS-over-HTTPS or other custom transports are enabled.
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-2026-80987

No EUVD known-exploited evidence

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

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
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 3 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

What

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

Why

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

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

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

Why

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

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.
Reference recorded

CISA Vulnrichment records proof-of-concept exploitation in its SSVC data. BlackTree has not independently executed or validated exploit material.

Likely attack path
a network path → Allocation of Resources Without Limits or Throttling → 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
Low: no specialised conditions are recorded
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-770 ↗

CWE-770: Allocation of Resources Without Limits or Throttling. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

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:L/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.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.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-770Public exploit reference
A

Official authority intelligence

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

ENISA EUVD · EUVD-2026-80987Official EUVD mapping

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

Official EUVD record ↗
BSI · German · WID-SEC-2026-3104CoreDNS: Schwachstelle ermöglicht Denial of Service

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in CoreDNS ausnutzen, um einen Denial of Service Angriff durchzuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260923Security Bulletin 23 Sep 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 23 Sep 2026, published on 23 September 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

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
1.14.7.
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
There is no complete mitigation available for this issue without upgrading. However, administrators can reduce risk by implementing the following interim measures: 1. If DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, or DNS-over-gRPC are not required, disable these custom transport protocols and use only standard UDP/TCP DNS, which is not affected by this vulnerability. 2. Implement network-level rate limiting for HTTPS and QUIC traffic to CoreDNS endpoints to reduce the effectiveness of concurrent memory exhaustion attacks. 3. Configure resource limits (memory limits) for CoreDNS pods to prevent a single CoreDNS instance from consuming all node memory, and ensure sufficient pod replicas for high availability. 4. Monitor CoreDNS memory usage and configure alerts for unusual memory consumption patterns or Out-of-Memory events. 5. Restrict network access to CoreDNS custom transport endpoints to trusted clients only using NetworkPolicies or firewall rules. Apply updates as they become available from Red Hat product teams. For OpenShift clusters, prioritize patching environments where DNS-over-HTTPS or other custom transports are enabled.
04

Evidence and provenance

Published 16 Sept 2026 · Last source change 18 Sept 2026, 18:19 UTC · CWE-770 · Allocation of Resources Without Limits or Throttling

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 2026-09-17
European sourceENISA EUVD · EUVD-2026-80987
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD awaiting enrichment

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
    rhacm2/lighthouse-coredns-rhel9 as a component of Red Hat Advanced Cluster Management for Kubernetes 2; rhcl-1/coredns-rhel9 as a component of Red Hat Connectivity Link 1; openshift4/ose-coredns as a component of Red Hat OpenShift Container Platform 4; openshift4/ose-coredns-rhel9 as a component of Red Hat OpenShift Container Platform 4
    After
    rhcl-1/coredns-rhel9 as a component of Red Hat Connectivity Link 1; openshift4/ose-coredns as a component of Red Hat OpenShift Container Platform 4; openshift4/ose-coredns-rhel9 as a component of Red Hat OpenShift Container Platform 4
    Red Hat Product Security ↗
  2. Vendor guidanceAuthoritative vendor guidance changed from remediation: access.redhat.com/CVE-2026-82399 to remediation: access.redhat.com/CVE-2026-82399.
    Before
    remediation: access.redhat.com/CVE-2026-82399
    After
    remediation: access.redhat.com/CVE-2026-82399
    Red Hat Product Security ↗
  3. Remediation statusRemediation status changed from Awaiting fix to Mitigation available.
    Before
    Awaiting fix
    After
    Mitigation available
    Red Hat Product Security ↗
  4. Affected versionsThe structured affected or fixed version information changed.
    Before
    rhacm2/lighthouse-agent-rhel9 as a component of Red Hat Advanced Cluster Management for Kubernetes 2; rhacm2/lighthouse-coredns-rhel9 as a component of Red Hat Advanced Cluster Management for Kubernetes 2; rhcl-1/coredns-rhel9 as a component of Red Hat Connectivity Link 1; openshift4/ose-coredns as a component of Red Hat OpenShift Container Platform 4; openshift4/ose-coredns-rhel9 as a component of Red Hat OpenShift Container Platform 4
    After
    rhacm2/lighthouse-coredns-rhel9 as a component of Red Hat Advanced Cluster Management for Kubernetes 2; rhcl-1/coredns-rhel9 as a component of Red Hat Connectivity Link 1; openshift4/ose-coredns as a component of Red Hat OpenShift Container Platform 4; openshift4/ose-coredns-rhel9 as a component of Red Hat OpenShift Container Platform 4
    Red Hat Product Security ↗
  5. Public exploit evidencePublic exploit evidence changed from No public exploit to Public exploit reference.
    Before
    No public exploit
    After
    Public exploit reference
    CVE.org ↗
  6. ENISA EUVD mappingEUVD-2026-80987 was added to the official ENISA EUVD mapping for this CVE.
    Before
    not recorded
    After
    {"euvdId":"EUVD-2026-80987"}
    ENISA EUVD ↗
  7. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-80987↗Vendor CSAF · Red Hat Product Security↗CISA Vulnrichment SSVC evidence↗CVE authority or vendor reference · GitHub GHSA-MRG3-QVQR-JW29↗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-2026-82399 · cve.blacktree.nl