Linux Kernel net/sched/cls_fw.c fw_change use after free

Summaryinfo

A vulnerability was found in Linux Kernel. It has been rated as critical. Affected is the function fw_change of the file net/sched/cls_fw.c. This manipulation causes use after free. The identification of this vulnerability is CVE-2023-4207. The attack can only be executed locally. There is no exploit available. Applying a patch is the recommended action to fix this issue.

Detailsinfo

A vulnerability was found in Linux Kernel (Operating System) (version unknown). It has been declared as critical. Affected by this vulnerability is the function fw_change of the file net/sched/cls_fw.c. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The weakness was shared 09/06/2023. The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2023-4207 since 08/07/2023. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 12/04/2025).

Applying a patch is able to eliminate this problem. The bugfix is ready for download at git.kernel.org.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2025-1293). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Ubuntu Linux
• IBM DataPower Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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