Linux Kernel up to 6.16.1/6.17-rc1 netfilter refcount_inc_not_zero memory leak

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.16.1/6.17-rc1. It has been classified as critical. This affects the function refcount_inc_not_zero of the component netfilter. The manipulation leads to memory leak. This vulnerability is traded as CVE-2025-39764. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.16.1/6.17-rc1 and classified as critical. This issue affects the function refcount_inc_not_zero of the component netfilter. The manipulation with an unknown input leads to a memory leak vulnerability. Using CWE to declare the problem leads to CWE-401. The product does not sufficiently track and release allocated memory after it has been used, which slowly consumes remaining memory. Impacted is availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: remove refcounting in expectation dumpers Same pattern as previous patch: do not keep the expectation object alive via refcount, only store a cookie value and then use that as the skip hint for dump resumption. AFAICS this has the same issue as the one resolved in the conntrack dumper, when we do if (!refcount_inc_not_zero(&exp->use)) to increment the refcount, there is a chance that exp == last, which causes a double-increment of the refcount and subsequent memory leak.

It is possible to read the advisory at git.kernel.org. The identification of this vulnerability is CVE-2025-39764 since 04/16/2025. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 264746 (Linux Distros Unpatched Vulnerability : CVE-2025-39764), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.16.2 or 6.17-rc2 eliminates this vulnerability. Applying a patch is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (264746) and CERT Bund (WID-SEC-2025-2040). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• Google Container-Optimized OS
• Debian Linux
• Google Cloud Platform
• Amazon Linux 2
• Red Hat Enterprise Linux
• Fedora Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel
• Proxmox Virtual Environment
• Proxmox Backup Server
• Dell Secure Connect Gateway
• IBM QRadar SIEM

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.16.0
• 6.16.1
• 6.17-rc1

License

• open-source

Website

• Vendor: https://www.kernel.org/

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