Bug 2536382 (CVE-2026-8674)

Summary: CVE-2026-8674 glibc: glibc DNS stub resolver: Denial of Service via long search domain in configuration
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, ashankar, codonell, dj, dpaolell, fweimer, jdelft, jupierce, lgarciaa, mbiarnes, pfrankli, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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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.
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Description OSIDB Bzimport 2026-09-17 17:37:50 UTC 
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.