Linux Kernel up to 6.18.15/6.19.5 tcp_v6_syn_recv_sock race condition

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.18.15/6.19.5. It has been classified as critical. Affected by this vulnerability is the function tcp_v6_syn_recv_sock. This manipulation causes race condition. This vulnerability is handled as CVE-2026-43198. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.18.15/6.19.5 and classified as critical. Affected by this vulnerability is the function tcp_v6_syn_recv_sock. The manipulation with an unknown input leads to a race condition vulnerability. The CWE definition for the vulnerability is CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. The impact remains unknown. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: tcp: fix potential race in tcp_v6_syn_recv_sock() Code in tcp_v6_syn_recv_sock() after the call to tcp_v4_syn_recv_sock() is done too late. After tcp_v4_syn_recv_sock(), the child socket is already visible from TCP ehash table and other cpus might use it. Since newinet->pinet6 is still pointing to the listener ipv6_pinfo bad things can happen as syzbot found. Move the problematic code in tcp_v6_mapped_child_init() and call this new helper from tcp_v4_syn_recv_sock() before the ehash insertion. This allows the removal of one tcp_sync_mss(), since tcp_v4_syn_recv_sock() will call it with the correct context.

It is possible to read the advisory at git.kernel.org. This vulnerability is known as CVE-2026-43198 since 05/01/2026. The exploitation appears to be difficult. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 321690 (SUSE SLES12 Security Update : kernel (SUSE-SU-2026:2450-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.18.16 or 6.19.6 eliminates this vulnerability. Applying the patch fe89b2f05b854847784f91127319172945c1fadd/7178e2a8027423b2af17ab95df73a749a5b72e5b/858d2a4f67ff69e645a43487ef7ea7f28f06deae 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 vulnerability database at Tenable (321690). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.18.0
• 6.18.1
• 6.18.2
• 6.18.3
• 6.18.4
• 6.18.5
• 6.18.6
• 6.18.7
• 6.18.8
• 6.18.9
• 6.18.10
• 6.18.11
• 6.18.12
• 6.18.13
• 6.18.14
• 6.18.15
• 6.19.0
• 6.19.1
• 6.19.2
• 6.19.3
• 6.19.4
• 6.19.5

License

• open-source

Website

• Vendor: https://www.kernel.org/

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