# CVE-2026-3104: ISC BIND 9 memory leak in DNSSEC proof-of-non-existence code

Source: https://junglewise.ai/threats/cve-2026-3104-isc-bind-9-memory-leak-in-dnssec-proof-of-non-existence-code  
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-2026-3104 · Severity: high · CVSS 7.5 · Published 2026-03-25

BIND 9 is a widely used software suite for managing Domain Name System (DNS) services. A vulnerability in its resolver component allows an attacker to cause a memory leak by requesting information about a specially crafted domain. Over time, this can exhaust the server's available memory, leading to a service crash or system instability, effectively knocking the DNS server offline.

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

## Quick answers

**Is CVE-2026-3104 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-3104 being exploited in the wild.

**How severe is CVE-2026-3104?** High severity, with a CVSS score of 7.5, published 25 March 2026.

**Which products and versions are affected?** Isc BIND 9 9.20.0 through 9.20.20, 9.21.0 through 9.21.19, 9.20.9-S1 through 9.20.20-S1.

**Is there a fix for CVE-2026-3104?** A patch was published on 2026-03-25: Patched versions 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-2026-3104 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-3104?** 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 memory leak exists in BIND 9 within the code responsible for preparing DNSSEC proofs of non-existence. The vulnerability is classified as a missing release of memory (CWE-401/CWE-772) and can be triggered remotely by an unauthenticated attacker who sends a query for a specially crafted domain to an affected BIND resolver. This results in unbounded growth of Resident Set Size (RSS) memory, eventually causing an out-of-memory (OOM) condition. Additionally, the 'named' process will exit with an assertion failure if a shutdown or reload is attempted while in this state. Authoritative-only servers are generally unaffected. Patches are available in versions 9.20.21 and 9.21.20.

## Affected products

- ISC BIND 9 9.20.0 through 9.20.20, 9.21.0 through 9.21.19, 9.20.9-S1 through 9.20.20-S1

## Timeline

- 2026-03-18: other: Early notification provided
- 2026-03-25: disclosed: Public disclosure and advisory published
- 2026-03-25: patched: Patched versions 9.20.21 and 9.21.20 released

## References

- [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-2026-3104](https://kb.isc.org/docs/cve-2026-3104)

## 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)