CVE-2026-23105

A flaw was found in the Linux kernel's Quick Fair Queuing (QFQ) scheduler. The QFQ class deactivation logic incorrectly relies on a child qdisc's queue length (qlen) to determine if a class is active. A local user with CAP_NET_ADMIN capabilities can manipulate the child qlen into an unexpected state. This manipulation can destabilize the scheduling behavior, leading to traffic disruption or a Denial of Service (DoS) in the networking stack.

QFQ class deactivation logic used a child qdisc qlen check to decide whether a class is active. If a child qlen can be manipulated into an unexpected state then QFQ may deactivate or keep a class in an inconsistent way which can destabilize scheduling behavior. This can lead to traffic disruption or a denial of service through scheduler inconsistency rather than memory corruption. For the CVSS the PR is L in the paranoid rating because CAP_NET_ADMIN can be delegated in some environments and it is sufficient to create and modify qdiscs. The issue is not directly network reachable because it requires local control plane configuration of traffic control objects. Impact is primarily denial of service in the networking stack and not a confidentiality or integrity breach.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.