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CVE-2025-21702 is an incorrect queue-length accounting vulnerability in the Linux kernel traffic-control subsystem. In pfifo_tail_enqueue(), a pfifo_head_drop qdisc configured with a zero packet limit can accept a packet when its queue is empty, increment the child qdisc queue length, and return NET_XMIT_CN even though no existing packet was dropped. A parent qdisc, including HFSC or DRR, can treat that result as non-success and not increment its own queue length. This produces an inconsistent hierarchy in which a parent qdisc's qlen does not equal the aggregate qlen of its children.
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Linux kernel packet scheduler limit-handling flaw.
A resolved Linux kernel network traffic-control qdisc accounting flaw in pfifo_tail_enqueue() when sch->limit equals zero. The condition can desynchronize parent and child qdisc queue-length accounting and, when reachable, may enable local user-to-kernel privilege escalation.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.