Heap Overflow in Unbound DNSCrypt TCP Handling (CVE-2026-40691)

A heap overflow vulnerability exists in Unbound when compiled with DNSCrypt support. A malicious DNSCrypt query over TCP causes the reply encryption routine to fail to bound the reply length against the destination buffer, leading to an out-of-bounds write. A single such query can crash the resolver, resulting in denial of service. Affected versions: - 1.9.0 up to and including version 1.25.1 We recommend updating to: 1.25.2. CVSS 7.5 · our assessment: this_week Reference: https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40691.txt Details: https://vuln.today/cve/CVE-2026-40691