Heap Overflow Vulnerability in NLnet Labs Unbound DNS Resolver

CVE-2026-42944

What is CVE-2026-42944?

NLnet Labs Unbound versions from 1.14.0 to 1.25.0 are susceptible to a heap overflow vulnerability when multiple NSID, DNS Cookie EDNS, or EDNS Padding options are enabled in response packets. This flaw arises from improper size calculations in the EDNS fields, leading to overflow conditions that could allow an attacker to crash the Unbound service. An attacker capable of querying the Unbound service can exploit this vulnerability by manipulating the query to include multiple relevant EDNS options. The issue is mitigated in Unbound version 1.25.1, which implements mechanisms to de-duplicate EDNS options and rectify the size calculation errors.

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