Linux Kernel up to 6.18.2/6.19-rc1 inet fqdir_pre_exit deadlock

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.18.2/6.19-rc1 and classified as critical. This vulnerability affects the function fqdir_pre_exit of the component inet. The manipulation results in deadlock. This vulnerability is identified as CVE-2025-68768. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel up to 6.18.2/6.19-rc1. Affected is the function fqdir_pre_exit of the component inet. The manipulation with an unknown input leads to a deadlock vulnerability. CWE is classifying the issue as CWE-833. The product contains multiple threads or executable segments that are waiting for each other to release a necessary lock, resulting in deadlock. This is going to have an impact on availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: inet: frags: flush pending skbs in fqdir_pre_exit() We have been seeing occasional deadlocks on pernet_ops_rwsem since September in NIPA. The stuck task was usually modprobe (often loading a driver like ipvlan), trying to take the lock as a Writer. lockdep does not track readers for rwsems so the read wasn't obvious from the reports. On closer inspection the Reader holding the lock was conntrack looping forever in nf_conntrack_cleanup_net_list(). Based on past experience with occasional NIPA crashes I looked thru the tests which run before the crash and noticed that the crash follows ip_defrag.sh. An immediate red flag. Scouring thru (de)fragmentation queues reveals skbs sitting around, holding conntrack references. The problem is that since conntrack depends on nf_defrag_ipv6, nf_defrag_ipv6 will load first. Since nf_defrag_ipv6 loads first its netns exit hooks run _after_ conntrack's netns exit hook. Flush all fragment queue SKBs during fqdir_pre_exit() to release conntrack references before conntrack cleanup runs. Also flush the queues in timer expiry handlers when they discover fqdir->dead is set, in case packet sneaks in while we're running the pre_exit flush. The commit under Fixes is not exactly the culprit, but I think previously the timer firing would eventually unblock the spinning conntrack.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2025-68768 since 12/24/2025. The exploitability is told to be difficult. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 298917 (SUSE SLES15 Security Update : kernel (SUSE-SU-2026:0472-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.18.3 or 6.19-rc2 eliminates this vulnerability. Applying the patch c70df25214ac9b32b53e18e6ae3b8f073ffa6903/006a5035b495dec008805df249f92c22c89c3d2e 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 (298917) and CERT Bund (WID-SEC-2026-0086). Once again VulDB remains the best source for vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.18.0
• 6.18.1
• 6.18.2
• 6.19-rc1

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Once again VulDB remains the best source for vulnerability data.

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