c-ares: Memory-amplification denial of service via unvalidated DNS header record counts (CVE-2026-69186)
Published Last modified Sources: SUSE, Ubuntu, Red Hat, CVE.org, Msrc Update Guide
What is affected, what to do
A flaw was found in c-ares, an asynchronous resolver library. A remote attacker can send a specially crafted DNS response that causes the `ares_dns_parse()` function to trust attacker-controlled record counts without validating if the response contains enough bytes for the claimed records.
Update C-ares to version 1.34.7.
- Affected
- C-ares
lt *..1.34.7
- C-ares
- Fixed in
- C-ares
1.34.7
- C-ares
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Metrics
5.3
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
5.3
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: SUSE, Ubuntu, Red Hat, CVE.org, Msrc Update Guide
0.5 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 40.5
Show all metrics
- Severity
- Medium
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 66.10 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 5.3 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 5.3
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.5 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 40.5
- High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
- CISA assessment (SSVC)
- Exploitation: proof of concept · automatable · Technical impact: partial
- Source: CISA Vulnrichment, as of 18 September 2026
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-400
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
A flaw was found in c-ares, an asynchronous resolver library. A remote attacker can send a specially crafted DNS response that causes the `ares_dns_parse()` function to trust attacker-controlled record counts without validating if the response contains enough bytes for the claimed records. This can lead to disproportionate heap memory reservation, resulting in a memory-amplification denial of service (DoS) by degrading or denying name resolution.
Source: suse_csaf, Ubuntu Security Notices, redhat_csaf, NVD (NIST), CVE.org (MITRE), cvelistv5, Microsoft Security Update Guide
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| c-ares | c-ares |
|
|
Vendors and products
Affected operating systems
| Linux | ubuntu | c-ares | bionic |
| Linux | ubuntu | c-ares | focal |
| Linux | ubuntu | c-ares | jammy |
| Linux | ubuntu | c-ares | noble |
| Linux | ubuntu | c-ares | resolute |
| Linux | ubuntu | c-ares | xenial |
Weakness classes (CWE)
CWE-400Uncontrolled Resource Consumption
Class
The product does not properly control the allocation and maintenance of a limited resource.
Entry at MITRE CWE-400
References & sources
- github.comc-ares/c-ares/security/advisories/GHSA-jv8r-gqr9-68wjx_refsource_CONFIRM
- github.comc-ares/c-ares/pull/1134x_refsource_MISC
- github.comc-ares/c-ares/commit/e47c203f91cd8b749c8736bc18d75a31ffdec8f4x_refsource_MISC
- github.comc-ares/c-ares/commit/eaded4cb200b2a5f8d73f11021ff7c8d6968aaabx_refsource_MISC
- github.comc-ares/c-ares/releases/tag/v1.34.7x_refsource_MISC
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedCISA ADP
CISA assessment (SSVC): exploitation: proof of concept, automatable: yes
Show 2 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://github.com/c-ares/c-ares/security/advisories/GHSA-jv8r-gqr9-68wjSSVC assessment added —{"id":"CVE-2026-69186","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-18T19:50:58.245833Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
ReceivedGitHub
CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness type: CWE-400
Description added or changed
Show 9 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —c-ares is an asynchronous resolver library. Prior to 1.34.7, ares_dns_parse() trusts the attacker-controlled ANCOUNT, NSCOUNT, and ARCOUNT fields before confirming that the DNS response contains enough bytes for the claimed records. Because process_answer() invokes parsing before transaction ID and question validation, a malicious DNS response can cause ares_dns_record_rr_prealloc() and ares_array_set_size() to reserve disproportionate heap memory for a tiny message. Repeated responses create large allocation and release cycles that can degrade or deny name resolution, without causing memory corruption or information disclosure. This issue is fixed in version 1.34.7.CVSS added —AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LWeakness type (CWE) added —CWE-400Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/69xxx/CVE-2026-69186.json">CVE-2026-69186</a>Reference added —https://github.com/c-ares/c-ares/commit/e47c203f91cd8b749c8736bc18d75a31ffdec8f4Reference added —https://github.com/c-ares/c-ares/commit/eaded4cb200b2a5f8d73f11021ff7c8d6968aaabReference added —https://github.com/c-ares/c-ares/pull/1134Reference added —https://github.com/c-ares/c-ares/releases/tag/v1.34.7Reference added —https://github.com/c-ares/c-ares/security/advisories/GHSA-jv8r-gqr9-68wjSource identifier: security-advisories@github.com
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-69186"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-69186.svg?lang=en" alt="CVE-2026-69186 – NEOSEC Intel" height="20"></a>