Assertion failure in the DNS stub resolver with a long search domain (CVE-2026-8674)
Published Last modified Sources: Red Hat, SUSE, BSI, CVE.org, Msrc Update Guide
What is affected, what to do
A flaw was found in the GNU C Library (glibc) DNS stub resolver. This vulnerability allows a remote attacker on the local network to cause a denial of service by providing a specially crafted, excessively long search domain.
The available sources name no fixed version. Check the vendor guidance in the references below.
- Affected
- The GNU C Library Glibc
lte 2.26..2.44
- The GNU C Library Glibc
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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: Red Hat, SUSE, BSI, CVE.org, Msrc Update Guide
0.3 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 24.3
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- 61.21 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- 0.3 %
- 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- 24.3
- Elevated — this CVE ranks above at least 10% of all CVEs scored today.
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
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-617
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 the GNU C Library (glibc) DNS stub resolver. This vulnerability allows a remote attacker on the local network to cause a denial of service by providing a specially crafted, excessively long search domain. When the resolver attempts to initialize with this long domain from /etc/resolv.conf or the LOCALDOMAIN environment variable, it triggers an assertion failure, which aborts the process. This can be exploited without privileges on the target system, potentially through network configuration mechanisms like DHCP or a VPN server.
Source: redhat_csaf, suse_csaf, BSI WID Portal, BSI CSAF, NVD (NIST), 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 | ||
|---|---|---|---|
| The GNU C Library | glibc |
|
|
Vendors and products
Weakness classes (CWE)
CWE-617Reachable Assertion
Base
The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.
Entry at MITRE CWE-617
References & sources
- sourceware.orgbugzilla/show_bug.cgi?id=31026Issue tracking
- sourceware.orggit/?p=glibc.git;a=blob_plain;f=advisories/GLIBC-SA-2026-0021Vendor advisory
- sourceware.orggit/?p=glibc.git;a=commit;h=506ea57086bfb9ce3daff1c14246a1cb532…Patch
- joshua.hufuzzing-glibc-libresolvTechnical description
- openwall.comlists/oss-security/2026/09/17/4
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: none known, automatable: no
Show the original change
Individual changes of this event as published by NVD Type Action Before After SSVC assessment added —{"id":"CVE-2026-8674","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-17T18:05:54.714741Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Record modifiedCVE Program
New references:Show the original change
Individual changes of this event as published by NVD Type Action Before After Reference added —http://www.openwall.com/lists/oss-security/2026/09/17/4Source identifier: af854a3a-2127-422b-91ae-364da2661108
Received3ff69d7a…
CVSS V3.1: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness type: CWE-617
Description added or changed
Show 8 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —Initializing the DNS stub resolver from an /etc/resolv.conf file, or a LOCALDOMAIN environment variable, whose search list contains a domain of roughly 200 characters or more in the GNU C Library version 2.26 to 2.44 results in an assertion failure which aborts the process. The resolver truncates the search list when copying it into the fixed-size _res.defdname buffer, then asserts that the copy is consistent with the full configuration. The consistency check compared against the wrong size and did not handle a first entry that does not fit, so a correctly truncated list failed the assertion. Any process that resolves names through the library is affected, including long-running processes that reload /etc/resolv.conf on the next query after it changes. Search domains are commonly written to /etc/resolv.conf from data received over DHCP or from a VPN server, so an attacker on the local network may be able to trigger this without privileges on the target system, subject to validation by the network configuration software.CVSS added —AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:HWeakness type (CWE) added —CWE-617Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/8xxx/CVE-2026-8674.json">CVE-2026-8674</a>Reference added —https://joshua.hu/fuzzing-glibc-libresolvReference added —https://sourceware.org/bugzilla/show_bug.cgi?id=31026Reference added —https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=advisories/GLIBC-SA-2026-0021Reference added —https://sourceware.org/git/?p=glibc.git;a=commit;h=506ea57086bfb9ce3daff1c14246a1cb532aba0aSource identifier: 3ff69d7a-14f2-4f67-a097-88dee7810d18
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-8674"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-8674.svg?lang=en" alt="CVE-2026-8674 – NEOSEC Intel" height="20"></a>