# CVE-2026-97313: ISC BIND recursive server assert failure denial of service

Source: https://junglewise.ai/threats/cve-2026-97313-a-recursive-bind-server-that-receives-a-query-with-recursion  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-21. Updated: 2026-10-21  
License: CC BY 4.0 with a link back

CVE-2026-97313 · Severity: high · CVSS 7.5 · Published 2026-10-21

BIND is a DNS server that many organizations rely on to translate domain names to IP addresses. A flaw in BIND's recursive query handling can cause the server to crash with an assertion failure when it receives specific sequences of DNS queries, resulting in a denial of service that disrupts DNS resolution for all clients relying on that server.

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

## Quick answers

**Is CVE-2026-97313 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-97313 being exploited in the wild.

**How severe is CVE-2026-97313?** High severity, with a CVSS score of 7.5, published 21 October 2026.

**Which products and versions are affected?** Isc BIND 9 9.11.3-S1 through 9.18.50-S1, 9.16.0 through 9.18.50, 9.20.0 through 9.20.29, 9.20.9-S1 through 9.20.29-S1, 9.21.0 through 9.21.26.

**Is there a fix for CVE-2026-97313?** Yes: fixed in BIND 9.18.51, 9.20.30, 9.21.27. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-97313 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-97313?** 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.

## How to fix

- Fixed in BIND 9.18.51, 9.20.30, 9.21.27

## Technical details

A recursive BIND server crashes with an assertion failure when it processes a query with recursion desired (RD=1) followed by a non-recursive query (RD=0), but only if the server has at least two RPZ (Response Policy Zone) zones configured with mismatched "recursive-only" settings. The vulnerability is triggered by the specific query sequence and RPZ configuration combination, causing an unhandled assertion that terminates the server process.

## Affected products

- ISC BIND 9 9.11.3-S1 through 9.18.50-S1, 9.16.0 through 9.18.50, 9.20.0 through 9.20.29, 9.20.9-S1 through 9.20.29-S1, 9.21.0 through 9.21.26

## Timeline

- 2026-10-21: disclosed
- 2026-10-21: patched

## References

- [https://downloads.isc.org/isc/bind9/9.20.30](https://downloads.isc.org/isc/bind9/9.20.30)
- [https://downloads.isc.org/isc/bind9/9.21.27](https://downloads.isc.org/isc/bind9/9.21.27)

## Related threats

- [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)
- [ISC BIND 9 resource exhaustion in DNSSEC validating resolver](https://junglewise.ai/threats/cve-2026-11622-isc-bind-9-resource-exhaustion-in-dnssec-validating-resolver)