CVE-2023-4623: Use-after-free in Linux kernel's net/sched: sch_hfsc (HFSC qdisc traffic control) component

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-09-06 · updated 2026-10-14
Weakness: CWE-416

Description

A use-after-free vulnerability in the Linux kernel's net/sched: sch_hfsc (HFSC qdisc traffic control) component can be exploited to achieve local privilege escalation. If a class with a link-sharing curve (i.e. with the HFSC_FSC flag set) has a parent without a link-sharing curve, then init_vf() will call vttree_insert() on the parent, but vttree_remove() will be skipped in update_vf(). This leaves a dangling pointer that can cause a use-after-free. We recommend upgrading past commit b3d26c5702c7d6c45456326e56d2ccf3f103e60f.

Affected products

Debian Linux: 10.0
Linux kernel: from 2.6.12 before 4.14.327; from 4.15 before 4.19.295; from 4.20 before 5.4.257; from 5.5 before 5.10.195; from 5.11 before 5.15.132; from 5.16 before 6.1.53 — fixed in 4.14.327, 4.19.295, 5.10.195, 5.15.132, 5.4.257, 6.1.53

How to fix

Upgrade to a fixed version: Linux kernel 4.14.327, 4.19.295, 5.10.195, 5.15.132. Check the vendor advisory for mitigations.

References

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