CVE-2023-4207: Use-after-free in Linux kernel's net/sched: cls_fw 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 2026-06-17
Weakness: CWE-416

Description

A use-after-free vulnerability in the Linux kernel's net/sched: cls_fw component can be exploited to achieve local privilege escalation. When fw_change() is called on an existing filter, the whole tcf_result struct is always copied into the new instance of the filter. This causes a problem when updating a filter bound to a class, as tcf_unbind_filter() is always called on the old instance in the success path, decreasing filter_cnt of the still referenced class and allowing it to be deleted, leading to a use-after-free. We recommend upgrading past commit 76e42ae831991c828cffa8c37736ebfb831ad5ec.

Affected products

Debian Linux: 12.0
Linux kernel: from 3.18 before 4.14.326; from 4.15 before 4.19.295; from 4.20 before 5.4.253; from 5.5 before 5.10.190; from 5.11 before 5.15.126; from 5.16 before 6.1.45 — fixed in 4.14.326, 4.19.295, 5.10.190, 5.15.126, 5.4.253, 6.1.45

How to fix

Upgrade to a fixed version: Linux kernel 4.14.326, 4.19.295, 5.10.190, 5.15.126. Check the vendor advisory for mitigations.

References

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