# CVE-2026-81563: ISC BIND resolver resource exhaustion via SVCB/HTTPS AliasMode

Source: https://junglewise.ai/threats/cve-2026-81563-isc-bind-resolver-resource-exhaustion-via-svcb-https-aliasmode  
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-2026-81563 · Severity: high · CVSS 7.5 · Published 2026-09-16

ISC BIND is a widely-deployed DNS resolver used by organizations worldwide to translate domain names into IP addresses. A flaw in how BIND handles certain DNS record types (SVCB/HTTPS AliasMode) can cause it to leak internal memory when processing maliciously crafted DNS responses. Repeated exploitation exhausts resolver resources, eventually causing the DNS service to stop responding to legitimate queries and disrupting network connectivity for dependent systems.

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

## Quick answers

**Is CVE-2026-81563 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-81563 being exploited in the wild.

**How severe is CVE-2026-81563?** High severity, with a CVSS score of 7.5, published 16 September 2026.

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

**Is there a fix for CVE-2026-81563?** A patch was published on 2026-09-16: Patches released: BIND 9.18.51, 9.20.28, 9.21.26 and corresponding -S1 releases Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-81563 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-81563?** 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 resource leak in BIND's handling of SVCB/HTTPS AliasMode DNS records that reference 14 or more SVCB/HTTPS ServiceMode records. The resolver fails to properly deallocate internal data structures during processing of such records. An attacker can trigger this leak by crafting DNS responses containing malformed SVCB/HTTPS records; no authentication is required and the attack is triggered by network-reachable DNS queries. With repeated exploitation, memory exhaustion causes the resolver to deny service on new recursive lookups. Patches are available in BIND 9.18.51, 9.20.28, 9.21.26, and corresponding -S1 (security-only) maintenance releases.

## Affected products

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

## Timeline

- 2026-09-16: disclosed
- 2026-09-16: patched: Patches released: BIND 9.18.51, 9.20.28, 9.21.26 and corresponding -S1 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)