# CVE-2026-19666: ISC BIND dns64 malformed answer crash

Source: https://junglewise.ai/threats/cve-2026-19666-isc-bind-dns64-malformed-answer-crash  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-16. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-19666 · Severity: high · CVSS 7.5 · Published 2026-09-16

BIND is a widely-used DNS resolver software that translates domain names into IP addresses for internet connectivity. On resolvers configured with the dns64 feature (used for IPv6/IPv4 translation), a specially crafted malformed DNS response from an authoritative server can cause the BIND process to crash unexpectedly, resulting in a complete service outage and loss of DNS resolution capability for affected clients.

Technologies: [Isc Bind](https://junglewise.ai/threats/technologies/bind). Vendors: [Isc](https://junglewise.ai/threats/vendors/isc).

## Quick answers

**Is CVE-2026-19666 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-19666 being exploited in the wild.

**How severe is CVE-2026-19666?** High severity, with a CVSS score of 7.5, published 16 September 2026.

**Which products and versions are affected?** Isc Bind 9.11.0–9.18.50, 9.11.3-S1–9.18.50-S1, 9.20.0–9.20.27, 9.20.9-S1–9.20.27-S1, 9.21.0–9.21.25.

**Is there a fix for CVE-2026-19666?** A patch was published on 2026-09-16: Patches released: BIND 9.18.51, 9.20.28, 9.20.28-S2, 9.21.26 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-19666 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-19666?** Check whether you run Isc Bind at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This is a denial-of-service vulnerability in BIND's dns64 functionality. When a resolver processes a malformed DNS answer from an authoritative server—specifically one that is malformed in a particular way—and dns64 is enabled, the named process crashes without proper error handling. The vulnerability is triggered by parsing a network-reachable response from an authoritative DNS server; no authentication or special client privileges are required. The attack vector is network-based, and an attacker can cause service disruption by controlling or spoofing responses from an authoritative server. Patches are available in BIND 9.18.51, 9.20.28, 9.20.28-S2, and 9.21.26.

## Affected products

- ISC BIND 9.11.0–9.18.50, 9.11.3-S1–9.18.50-S1, 9.20.0–9.20.27, 9.20.9-S1–9.20.27-S1, 9.21.0–9.21.25

## Timeline

- 2026-09-16: disclosed
- 2026-09-16: patched: Patches released: BIND 9.18.51, 9.20.28, 9.20.28-S2, 9.21.26

## References

- [https://downloads.isc.org/isc/bind9/9.20.29](https://downloads.isc.org/isc/bind9/9.20.29)
- [https://downloads.isc.org/isc/bind9/9.21.26](https://downloads.isc.org/isc/bind9/9.21.26)

## Related threats

- [BIND assertion failure with redirect zone and qname-minimization](https://junglewise.ai/threats/cve-2026-96888-a-bind-resolver-that-is-configured-with-both-a-redirect-zone-and)
- [BIND named GSS-TSIG replay heap corruption](https://junglewise.ai/threats/cve-2026-94300-replaying-gss-tsig-signed-udp-messages-can-result-in-memory)
- [ISC BIND resolver DNS message processing denial of service](https://junglewise.ai/threats/cve-2026-19630-in-a-bind-resolver-inbound-dns-protocol-messages-with-a)
- [ISC BIND denial of service via TKEY queries](https://junglewise.ai/threats/cve-2015-5477-isc-bind-data-processing-errors-vulnerability)
- [BIND resolver crash on DNSSEC-signed wildcard with NSEC mismatch](https://junglewise.ai/threats/cve-2026-80274-bind-resolver-crash-on-dnssec-signed-wildcard-with-nsec-mismatch)