Bug 2436789 (CVE-2026-23105)

Summary: CVE-2026-23105 kernel: Linux kernel: Denial of Service in QFQ scheduler via child qlen manipulation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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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.
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Description OSIDB Bzimport 2026-02-04 17:03:28 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net/sched: qfq: Use cl_is_active to determine whether class is active in qfq_rm_from_ag

This is more of a preventive patch to make the code more consistent and
to prevent possible exploits that employ child qlen manipulations on qfq.
use cl_is_active instead of relying on the child qdisc's qlen to determine
class activation.
Comment 1 Jon Moroney 2026-02-04 23:31:12 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026020430-CVE-2026-23105-1d6d@gregkh/T