CVE-2026-8674: Assertion failure in the DNS stub resolver with a long search domain
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.
Affected Software
Event History
Frequently Asked Questions
Which systems and processes are realistically exposed?
Systems using GNU C Library versions 2.26 through 2.44 are affected when their resolver configuration includes a search-domain entry of roughly 200 characters or more. Any process that resolves names through the library can abort, including long-running processes that reload /etc/resolv.conf after it changes.
What does an attacker need to exploit this?
An attacker needs a way to cause the target to use a resolver search list containing an overly long domain. This may be possible from a local network through DHCP or from a VPN server, depending on whether the target's network configuration software validates received resolver settings.
Is administrator access on the target required?
Not necessarily. The issue can be triggered through /etc/resolv.conf data received via DHCP or a VPN server, so an attacker on the local network may be able to cause the condition without privileges on the target system.
How can I determine whether a system is currently at risk?
Check whether the system uses GNU C Library 2.26 through 2.44 and whether /etc/resolv.conf or the LOCALDOMAIN environment variable supplies a search-list domain of roughly 200 characters or more. Processes that perform DNS resolution after such configuration is initialized or reloaded may abort.