CVE-2026-4890

A denial of service vulnerability was discovered in dnsmasq's DNSSEC validation. When parsing NSEC and NSEC3 bitmap records, the window iteration logic fails to account for the 2-byte window header when advancing through the bitmap data. A specially crafted DNS response with a zero-length bitmap can cause an infinite loop, making dnsmasq unresponsive to all queries.

This issue affects deployments with DNSSEC validation enabled (--dnssec). The flaw is reachable before RRSIG signature validation, meaning no valid DNSSEC signatures are required to trigger it. However, the primary impact is limited to denial of service.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.