A use-after-free vulnerability exists within the DNS-over-HTTPS implementation. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9 versions 9.18.0 through 9.18.48 and 9.18.11-S1 through 9.18.48-S1 are NOT affected.
Weakness
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Bind | Isc | 9.20.0 (including) | 9.20.23 (excluding) |
| Bind | Isc | 9.21.0 (including) | 9.21.22 (excluding) |
| Red Hat Hardened Images | RedHat | bind-main-9.18.48-1.1.hum1 | * |
| Bind9 | Ubuntu | devel | * |
| Bind9 | Ubuntu | questing | * |
| Bind9 | Ubuntu | resolute | * |
| Bind9 | Ubuntu | upstream | * |
Potential Mitigations
References
- https://downloads.isc.org/isc/bind9/9.20.23
- https://downloads.isc.org/isc/bind9/9.21.22
- https://kb.isc.org/docs/cve-2026-3593
- https://access.redhat.com/errata/RHSA-2026:7412
- https://access.redhat.com/security/cve/CVE-2026-3593
- https://bugzilla.redhat.com/show_bug.cgi?id=2479770
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-3593.json