Executive brief
BIND is a widely-deployed DNS server that resolves domain names for millions of users and organizations. An attacker running an authoritative DNS server can craft a specially-sized response (exactly 65536 bytes) that causes BIND to create a corrupted cache entry. When BIND later tries to read this entry, the server crashes, causing DNS resolution to fail for affected customers.
Technical details
The vulnerability is a denial-of-service flaw in the negative cache handling logic of BIND's `named` resolver. When an attacker-controlled authoritative DNS server responds with a negative answer (NXDOMAIN or NODATA) that is exactly 65536 bytes in size, a bug in the cache entry creation causes the negative cache entry to be allocated with 0 bytes. Subsequently, when `named` attempts to read this malformed cache entry, it triggers an abort condition. The attack requires the victim to query a domain controlled by an attacker; no authentication is required. Patches are available in BIND 9.20.29, 9.21.26, and later versions.
Affected products
- ISC BIND 9.11.0 through 9.18.50, 9.20.0 through 9.20.27, 9.21.0 through 9.21.25, 9.11.3-S1 through 9.18.50-S1, 9.20.9-S1 through 9.20.27-S1
Timeline
- 2026-09-16: disclosed: CVE-2026-19667 published
- 2026-09-16: patched: BIND 9.20.29 and 9.21.26 released with fix