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PatchSiren cyber security CVE debrief

CVE-2026-32665 NLnet Labs CVE debrief

A remote denial of service vulnerability exists in NLnet Labs Unbound 1.22.0 through 1.25.1 when DNS-over-QUIC (DoQ) is enabled. The vulnerability allows a remote client to bypass the 'quic-size' limit, leading to excessive memory allocation and potential denial of service for new DoQ clients. This issue arises from the first two bidirectional streams on a new QUIC connection (stream_id 0 and 4) bypassing the per-stream 'quic-size' gate entirely. Large input buffers are allocated later, after only the 2-byte length prefix has been received from the initial streams. Organizations should prioritize patching to prevent potential denial of service attacks.

Vendor
NLnet Labs
Product
Unbound
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-22
Original CVE updated
2026-07-22
Advisory published
2026-07-22
Advisory updated
2026-07-22

Who should care

Organizations using Unbound 1.22.0-1.25.1 with DoQ enabled should prioritize patching to prevent potential denial of service attacks. This includes reviewing and adjusting 'quic-size' limits as necessary, monitoring Unbound logs for unusual activity, and implementing rate limiting for QUIC connections. Security teams and vulnerability management teams should also review the vulnerability details and assess their exposure.

Technical summary

The vulnerability is caused by the first two bidirectional streams on a new QUIC connection (stream_id 0 and 4) bypassing the per-stream 'quic-size' gate entirely. Large input buffers are allocated later, after only the 2-byte length prefix has been received from the initial streams. A remote client can make Unbound exceed the configured 'quic-size' limit with low-cost input, potentially leading to denial of service for new DoQ clients. This issue can be mitigated by patching to version 1.25.2 or later, disabling DoQ support if not required, and implementing rate limiting for QUIC connections.

Defensive priority

High

Recommended defensive actions

  • Patch Unbound to version 1.25.2 or later
  • Disable DoQ support if not required
  • Monitor Unbound logs for unusual activity
  • Implement rate limiting for QUIC connections
  • Review and adjust 'quic-size' limits as necessary
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record was published on 2026-07-22T14:17:18.193Z and was last modified on 2026-07-22T20:33:11.590Z. The NVD entry is currently Undergoing Analysis. This information is based on the supplied source corpus and may be subject to change as more information becomes available. Defenders should verify the affected scope and severity with the official CVE record and NVD entry. The vulnerability affects Unbound 1.22.0 through 1.25.1 when DNS-over-QUIC (DoQ) is enabled.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-22T14:17:18.193Z and has not been modified since then. The NVD entry is currently Undergoing Analysis.