Vulnerability · Published Sep 16, 2026 · Assigned by NLnet Labs
CVE-2026-81634Possible heap buffer overflow during DNSSEC canonicalization
High 7.5
In plain English
A high-severity heap buffer overflow in Unbound from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 42% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | python3-unbound | 1.24.2-7.el10_2.6 | ALSA-2026:71419 |
| AlmaLinux:8 | python3-unbound | 1.16.2-5.14.el8_10.4 | ALSA-2026:70754 |
| AlmaLinux:9 | python3-unbound | 1.24.2-3.el9_8.8 | ALSA-2026:71487 |
| AlmaLinux:10 | unbound | 1.24.2-7.el10_2.6 | ALSA-2026:71419 |
| AlmaLinux:8 | unbound | 1.16.2-5.14.el8_10.4 | ALSA-2026:70754 |
| AlmaLinux:9 | unbound | 1.24.2-3.el9_8.8 | ALSA-2026:71487 |
| AlmaLinux:10 | unbound-anchor | 1.24.2-7.el10_2.6 | ALSA-2026:71419 |
| AlmaLinux:10 | unbound-devel | 1.24.2-7.el10_2.6 | ALSA-2026:71419 |
| AlmaLinux:8 | unbound-devel | 1.16.2-5.14.el8_10.4 | ALSA-2026:70754 |
| AlmaLinux:9 | unbound-devel | 1.24.2-3.el9_8.8 | ALSA-2026:71487 |
| AlmaLinux:10 | unbound-dracut | 1.24.2-7.el10_2.6 | ALSA-2026:71419 |
| AlmaLinux:9 | unbound-dracut | 1.24.2-3.el9_8.8 | ALSA-2026:71487 |
| AlmaLinux:10 | unbound-libs | 1.24.2-7.el10_2.6 | ALSA-2026:71419 |
| AlmaLinux:8 | unbound-libs | 1.16.2-5.14.el8_10.4 | ALSA-2026:70754 |
| AlmaLinux:9 | unbound-libs | 1.24.2-3.el9_8.8 | ALSA-2026:71487 |
| AlmaLinux:10 | unbound-utils | 1.24.2-7.el10_2.6 | ALSA-2026:71419 |
| Debian:12 | unbound | no fix listed | DEBIAN-CVE-2026-81634 |
| Debian:13 | unbound | 1.26.1-0+deb13u1 | DEBIAN-CVE-2026-81634 |
| Debian:14 | unbound | 1.26.1-1 | DEBIAN-CVE-2026-81634 |
| Rocky Linux:10 | unbound | 0:1.24.2-7.el10_2.6 | RLSA-2026:71419 |
| Rocky Linux:8 | unbound | 0:1.16.2-5.14.el8_10.4 | RLSA-2026:70754 |
| Rocky Linux:9 | unbound | 0:1.24.2-3.el9_8.8 | RLSA-2026:71487 |
| Ubuntu:22.04:LTS | unbound | 1.13.1-1ubuntu5.17 | UBUNTU-CVE-2026-81634 |
| Ubuntu:22.04:LTS | unbound | 1.13.1-1ubuntu5.17 | USN-8946-1 |
| Ubuntu:24.04:LTS | unbound | 1.19.2-1ubuntu3.12 | USN-8946-1 |
| Ubuntu:24.04:LTS | unbound | 1.19.2-1ubuntu3.12 | UBUNTU-CVE-2026-81634 |
| Ubuntu:26.04:LTS | unbound | 1.24.2-1ubuntu2.4 | USN-8946-1 |
| Ubuntu:26.04:LTS | unbound | 1.24.2-1ubuntu2.4 | UBUNTU-CVE-2026-81634 |
| Ubuntu:26.10 | unbound | no fix listed | UBUNTU-CVE-2026-81634 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| NLnet Labs | Unbound | 0 – before 1.26.1 |
Weakness: CWE-122 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-81634.txt vendor-advisory