CVE-2026-8674 in glibc
Summary
by MITRE • 09/17/2026
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.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the GNU C Library versions 2.26 through 2.44 represents a critical flaw within the DNS stub resolver implementation that leads to process termination via an assertion failure. This issue stems from improper handling of search domain lists when they exceed specific length thresholds, specifically involving domains with approximately two hundred characters or more. The core technical defect lies in how the library manages memory during the initialization phase where it copies configuration data into a fixed-size buffer known as _res.defdname. During this copy operation, the resolver truncates the search list to fit within the allocated space but subsequently performs a consistency check that compares the truncated result against an incorrect size parameter. This logical error means that even when the truncation is performed correctly and safely, the subsequent validation step fails because it expects data that no longer exists in its original form, triggering an assertion failure that abruptly aborts the running process.
From an operational perspective, this vulnerability affects any application or service on a Linux system that relies on the GNU C Library for DNS resolution. The impact is particularly severe for long-running processes such as daemons, web servers, and database services which may periodically reload their configuration files including /etc/resolv.conf to adapt to network changes. When these systems encounter a search domain list exceeding the critical length threshold during a name resolution query following a configuration reload, they will crash immediately. This results in a denial of service condition where legitimate users are unable to access resources hosted on or reachable through the affected system. The reliability of network-dependent applications is compromised because the failure occurs at the fundamental level of name resolution, preventing any further network communication for that process until it is restarted manually by an administrator.
The attack surface for this vulnerability is significant due to common networking practices in enterprise and home environments. Search domains are frequently configured dynamically via Dynamic Host Configuration Protocol DHCP or through Virtual Private Network VPN connections. Consequently, a malicious actor positioned on the local network segment can craft specific DNS configuration responses that include excessively long search domain entries. By injecting such malformed data into the DHCP lease or VPN tunnel setup process, an attacker can force target systems to write these oversized domains into /etc/resolv.conf. When any application subsequently attempts to resolve a hostname and triggers a reload of this file, the assertion failure is triggered without requiring local user privileges on the target machine. This allows for remote denial-of-service attacks against critical infrastructure components that depend on stable DNS resolution capabilities.
In terms of industry standard classifications, this vulnerability aligns with CWE-617 which refers to Reachable Assertion indicating a logic error where an internal consistency check fails due to improper state management or boundary handling. The exploitation vector corresponds to ATT&CK technique T1498 Network Denial of Service specifically within the context of resource exhaustion through configuration manipulation rather than traffic flooding. Mitigation strategies primarily involve updating the GNU C Library to patched versions that correct the size comparison logic in the resolver initialization routine. System administrators should also implement monitoring for unexpected process terminations related to libc and consider restricting DHCP server configurations or VPN gateway settings to validate domain name lengths before pushing them to client systems. Additionally, hardening network access controls can prevent unauthorized devices from injecting malicious DNS configuration parameters into the local network infrastructure thereby reducing the risk of exploitation by external actors on the same subnet.