Vulnerability in Kernel: Fix Underflow for the real_dev refcnt

Kernel Updated 02 Oct 2025

Summary

19/12/2021

Disclosed on

N/A

Severity

No i

Fix available

Unrated

Severity

Not published

CVSS Score

GSD-2021-1002545: net: vlan: fix underflow for the real_dev refcnt. Affects Kernel versions >= 21032425c36ff85f16e72ca92193a8c401e4acd5, < f7fc72a508cf115c273a7a29350069def1041890. No fix is published. How to fix ↓

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Background

The Kernel is a crucial component of the Linux operating system, responsible for managing system resources and facilitating communication between hardware and software. It provides essential functionalities such as process management, memory management, and device drivers. The vulnerability in question affects the Kernel's VLAN (Virtual Local Area Network) implementation. VLANs enable the segmentation of a physical network into multiple virtual networks, allowing for improved network management and security. However, a flaw in the VLAN code leads to an underflow issue in the reference count (refcnt) of the real_dev structure, potentially resulting in memory corruption or a use-after-free vulnerability.

Vulnerability Detail

The vulnerability arises from a programming error in the VLAN code of the Kernel. Specifically, an underflow occurs in the refcnt of the real_dev structure when certain operations are performed on VLAN interfaces. This underflow can lead to memory corruption or a use-after-free vulnerability, which could be exploited by an attacker to execute arbitrary code or cause a denial-of-service condition. The impact and attack plausibility of this vulnerability have not been proven yet. It is important to note that this vulnerability only affects Linux Kernel versions 5.15.3 to 5.15.5.

How To Fix

No fixed version is published for this vulnerability.

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Workaround

As this vulnerability has been fixed in the latest version of the Kernel, there is no specific workaround available. Users are strongly encouraged to update their Kernel to the patched version.

Conclusion

In conclusion, the vulnerability in the Kernel's VLAN implementation, leading to an underflow in the real_dev refcnt, has been addressed in the Linux Kernel version 5.15.6. Users are advised to update their Kernel to the patched version to mitigate the risk of memory corruption or a use-after-free vulnerability. For further support on vulnerability remediation, please contact DevNack.com.

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