# CVE-2026-81736: ISC BIND DNS resolver high CPU consumption via cached SVCB/HTTPS AliasMode records

Source: https://junglewise.ai/threats/cve-2026-81736-isc-bind-dns-resolver-high-cpu-consumption-via-cached-svcb-https  
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-2026-81736 · Severity: high · CVSS 7.5 · Published 2026-09-16

ISC BIND is a widely-deployed DNS resolver software used by internet service providers and enterprises to resolve domain names. A vulnerability in its handling of cached SVCB/HTTPS AliasMode records can cause the resolver to consume disproportionate CPU resources when responding to queries, potentially causing denial of service and degrading the performance of DNS resolution services that depend on it.

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

## Quick answers

**Is CVE-2026-81736 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-81736 being exploited in the wild.

**How severe is CVE-2026-81736?** High severity, with a CVSS score of 7.5, published 16 September 2026.

**Which products and versions are affected?** Isc Bind 9.18.0 through 9.18.50, 9.20.0 through 9.20.27, 9.21.0 through 9.21.25, 9.18.11-S1 through 9.18.50-S1, 9.20.9-S1 through 9.20.27-S1.

**Is there a fix for CVE-2026-81736?** A patch was published on 2026-09-16: BIND 9.20.29, 9.21.26, and corresponding security releases Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-81736 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-81736?** 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

The vulnerability is a denial-of-service condition in BIND's DNS resolver implementation. When a resolver has cached a tree of SVCB/HTTPS AliasMode records and receives a query for the root of that tree, it spends excessive CPU time constructing the response, resulting in high computational overhead. The attack requires that the resolver has already cached the vulnerable record structure, and an attacker can trigger the condition by sending a DNS query targeting the root of a cached SVCB/HTTPS AliasMode tree. The issue affects multiple active versions of BIND 9, and patches are available in BIND 9.20.29, 9.21.26, and corresponding security releases.

## Affected products

- ISC BIND 9.18.0 through 9.18.50, 9.20.0 through 9.20.27, 9.21.0 through 9.21.25, 9.18.11-S1 through 9.18.50-S1, 9.20.9-S1 through 9.20.27-S1

## Timeline

- 2026-09-16: disclosed
- 2026-09-16: patched: BIND 9.20.29, 9.21.26, and corresponding security releases

## 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)