# CVE-2026-1519: ISC BIND 9 denial of service via excessive NSEC3 iterations

Source: https://junglewise.ai/threats/cve-2026-1519-isc-bind-9-denial-of-service-via-excessive-nsec3-iterations  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-25. Updated: 2026-05-21  
License: CC BY 4.0 with a link back

CVE-2026-1519 · Severity: high · CVSS 7.5 · Published 2026-03-25

ISC BIND 9 is a widely used software for managing Domain Name System (DNS) services. A vulnerability in its security validation process allows a remote attacker to send specially crafted data that causes the server to consume excessive processor resources. This can lead to a significant slowdown or complete loss of DNS service, preventing users from accessing websites and other network resources.

Technologies: [Isc BIND 9](https://junglewise.ai/threats/technologies/bind-9). Vendors: [Isc](https://junglewise.ai/threats/vendors/isc).

## Quick answers

**Is CVE-2026-1519 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-1519 being exploited in the wild.

**How severe is CVE-2026-1519?** High severity, with a CVSS score of 7.5, published 25 March 2026.

**Which products and versions are affected?** Isc BIND 9 9.11.0 through 9.16.50, 9.18.0 through 9.18.46, 9.20.0 through 9.20.20, 9.21.0 through 9.21.19, 9.11.3-S1 through 9.16.50-S1, 9.18.11-S1 through 9.18.46-S1, 9.20.9-S1 through 9.20.20-S1.

**Is there a fix for CVE-2026-1519?** A patch was published on 2026-03-25: Patched versions 9.18.47, 9.20.21, and 9.21.20 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-1519 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-1519?** Check whether you run Isc BIND 9 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

A denial-of-service vulnerability exists in BIND 9 resolvers when performing DNSSEC validation. The issue is caused by unchecked input for loop conditions (CWE-606) during the validation of insecure delegations involving NSEC3 records. A remote attacker can provide a maliciously crafted zone with excessive NSEC3 iterations, forcing the resolver to spend an inordinate amount of CPU time on validation. This results in a sharp decrease in the number of queries per second (QPS) the resolver can handle. Authoritative-only servers are generally unaffected unless they are configured to perform recursive queries. Patches are available in versions 9.18.47, 9.20.21, and 9.21.20.

## Affected products

- ISC BIND 9 9.11.0 through 9.16.50, 9.18.0 through 9.18.46, 9.20.0 through 9.20.20, 9.21.0 through 9.21.19, 9.11.3-S1 through 9.16.50-S1, 9.18.11-S1 through 9.18.46-S1, 9.20.9-S1 through 9.20.20-S1

## Timeline

- 2026-03-18: other: Early notification provided to partners
- 2026-03-25: advisory: Public disclosure by ISC
- 2026-03-25: patched: Patched versions 9.18.47, 9.20.21, and 9.21.20 released
- 2026-04-13: other: Debian LTS advisory published

## References

- [https://downloads.isc.org/isc/bind9/9.18.47](https://downloads.isc.org/isc/bind9/9.18.47)
- [https://downloads.isc.org/isc/bind9/9.20.21](https://downloads.isc.org/isc/bind9/9.20.21)
- [https://downloads.isc.org/isc/bind9/9.21.20](https://downloads.isc.org/isc/bind9/9.21.20)
- [https://kb.isc.org/docs/cve-2026-1519](https://kb.isc.org/docs/cve-2026-1519)
- [https://lists.debian.org/debian-lts-announce/2026/04/msg00008.html](https://lists.debian.org/debian-lts-announce/2026/04/msg00008.html)

## Related threats

- [ISC BIND recursive server assert failure denial of service](https://junglewise.ai/threats/cve-2026-97313-a-recursive-bind-server-that-receives-a-query-with-recursion)
- [ISC BIND DNSSEC validation bypass in NSEC records](https://junglewise.ai/threats/cve-2026-13321-isc-bind-dnssec-validation-bypass-in-nsec-records)
- [ISC BIND 9 denial of service via NSEC and NSEC3 assertion failure](https://junglewise.ai/threats/cve-2026-13204-isc-bind-9-denial-of-service-via-nsec-and-nsec3-assertion-failure)
- [ISC BIND 9 denial of service via CNAME or DNAME record ordering](https://junglewise.ai/threats/cve-2026-12617-isc-bind-9-denial-of-service-via-cname-or-dname-record-ordering)
- [ISC BIND 9 cache poisoning via RRSIG label count discrepancy](https://junglewise.ai/threats/cve-2026-11721-isc-bind-9-cache-poisoning-via-rrsig-label-count-discrepancy)