Vulnerability · Published Jul 22, 2026 · Assigned by NLnet Labs
CVE-2026-32665Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass
High 7.5
In plain English
A high-severity security flaw 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 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream DNS-over-QUIC (DoQ) is enabled, the first two bidirectional streams on a new QUIC connection (stream_id 0 and 4) bypass the per-stream 'quic-size' gate entirely, and large input buffers are allocated later, after only the 2-byte length prefix has been received from the initial streams. As a result, a remote client can make Unbound exceed the configured 'quic-size' limit with low-cost input. Using only one connection and two streams, each sending a declared 65535-byte length prefix and then holding the streams open, a client can already trivially make Unbound roughly allocate double that amount. This is a remote availability issue / memory-accounting bypass in the downstream DoQ implementation that leads to denial of service for new DoQ clients. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | unbound | no fix listed | DEBIAN-CVE-2026-32665 |
| Debian:13 | unbound | 1.26.1-0+deb13u1 | DEBIAN-CVE-2026-32665 |
| Debian:14 | unbound | 1.25.2-1 | DEBIAN-CVE-2026-32665 |
| 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:26.04:LTS | unbound | 1.24.2-1ubuntu2.4 | USN-8946-1 |
| Ubuntu:26.04:LTS | unbound | 1.24.2-1ubuntu2.4 | UBUNTU-CVE-2026-32665 |
| Ubuntu:26.10 | unbound | no fix listed | UBUNTU-CVE-2026-32665 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| NLnet Labs | Unbound | 1.22.0 – before 1.25.2 |
Weakness: CWE-1284 · 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-2026-32665.txt vendor-advisory