Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass
Summary
| CVE | CVE-2026-32665 |
|---|---|
| State | PUBLISHED |
| Assigner | NLnet Labs |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-07-22 14:17:18 UTC |
| Updated | 2026-07-22 20:33:11 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 7.5 HIGH from [email protected]
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Problem Types: CWE-1284 | CWE-1284 CWE-1284: Improper Validation of Specified Quantity in Input
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | CNA | CVSS | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | NLnet Labs | Unbound | affected 1.22.0 1.25.2 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt | [email protected] | www.nlnetlabs.nl | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: N0zoM1z0 (GitHub user) (en)
CNA: Kunta Chu (Tsinghua University) (en)
CNA: Kaihua Wang (Tsinghua University) (en)
CNA: Jianjun Chen (Tsinghua University) (en)
CNA: Qifan Zhang (Palo Alto Networks) (en)
CNA: Xuanchao Xie (en)
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| CNA | 2026-04-01T00:00:00.000Z | Issue reported by N0zoM1z0 |
| CNA | 2026-04-03T00:00:00.000Z | NLnet Labs shares patch with N0zoM1z0 |
| CNA | 2026-04-03T00:00:00.000Z | N0zoM1z0 verifies patch |
| CNA | 2026-04-03T00:00:00.000Z | Issue reported by Kunta Chu |
| CNA | 2026-04-09T00:00:00.000Z | NLnet Labs shares patch with Kunta Chu |
| CNA | 2026-04-03T00:00:00.000Z | Kunta Chu verifies patch |
| CNA | 2026-05-30T00:00:00.000Z | Issue reported by Qifan Zhang |
| CNA | 2026-06-15T00:00:00.000Z | NLnet Labs shares patch with Qifan Zhang |
| CNA | 2026-06-17T00:00:00.000Z | Qifan Zhang verifies patch |
| CNA | 2026-07-10T00:00:00.000Z | Issue reported by Xuanchao Xie |
| CNA | 2026-07-10T00:00:00.000Z | NLnet Labs shares patch with Xuanchao Xie |
| CNA | 2026-07-11T00:00:00.000Z | Xuanchao Xie verifies patch |
| CNA | 2026-07-22T00:00:00.000Z | Fixes released with version 1.25.2 |
Solutions
CNA: This issue is fixed starting with version 1.25.2
There are currently no legacy QID mappings associated with this CVE.