CVE-2025-68325: net/sched: sch_cake: Fix incorrect qlen reduction in cake_drop

Severity: unknown
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-12-18 · updated 2026-10-13

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_cake: Fix incorrect qlen reduction in cake_drop In cake_drop(), qdisc_tree_reduce_backlog() is used to update the qlen and backlog of the qdisc hierarchy. Its caller, cake_enqueue(), assumes that the parent qdisc will enqueue the current packet. However, this assumption breaks when cake_enqueue() returns NET_XMIT_CN: the parent qdisc stops enqueuing current packet, leaving the tree qlen/backlog accounting inconsistent. This mismatch can lead to a NULL dereference (e.g., when the parent Qdisc is qfq_qdisc). This patch computes the qlen/backlog delta in a more robust way by observing the difference before and after the series of cake_drop() calls, and then compensates the qdisc tree accounting if cake_enqueue() returns NET_XMIT_CN. To ensure correct compensation when ACK thinning is enabled, a new variable is introduced to keep qlen unchanged.

Affected products

Linux kernel: from 5.10.241 before 5.10.248; from 5.15.190 before 5.15.198; from 6.1.149 before 6.1.160; from 6.6.103 before 6.6.120; from 6.12.44 before 6.12.63; from 5.4.297 before 5.5 — fixed in 5.10.248, 5.15.198, 5.5, 6.1.160, 6.12.63, 6.17

How to fix

Upgrade to a fixed version: Linux kernel 5.10.248, 5.15.198, 5.5, 6.1.160. Check the vendor advisory for mitigations.

References

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