CVE-2026-41637

Public on 2026-07-22
Modified on 2026-07-27
Description
In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted properly by Unbound resulting in low-cost inflation of the waiting number of replies for already in-flight resolution queries. This results in degradation of resolution service for new clients for already in-flight queries. A malicious actor can exploit the vulnerability by issuing DoQ queries for query names that need resolution and proceeding on immediately terminating the query by one of STOP_SENDING/RESET_STREAM/CONNECTION_CLOSE QUIC frames. Those terminated DoQ queries are not properly counted for and keep inflating the number of waiting replies for in-flight queries. When the maximum is reached, it results in silent query drops for new clients needing resolution for already in-flight queries. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces. Additionally, a malicious actor needs access to multiple source IPs to bypass the by-default configured 'wait-limit' option.
Severity
Low severity
Low
See what this means
CVSS v3 Base Score
3.7
See breakdown

Affected Packages

Platform Package Release Date Advisory Status
Amazon Linux 2 - Core unbound Not Affected
Amazon Linux 2 - Unbound1.17 Extra unbound Not Affected
Amazon Linux 2023 unbound Not Affected

CVSS Scores

Score Type Score Vector
Amazon Linux CVSSv3 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L