Use-after-free in Linux kernel IPv6 ip6_xmit()

Successful exploitation can trigger a kernel use-after-free in the IPv6 transmit path, resulting in memory corruption, kernel instability, or a system crash. Available scoring information indicates the issue is primarily a local vulnerability with high availability impact and low integrity impact. Depending on kernel state and exploitability in a given environment, use-after-free conditions in kernel networking code may also create a path toward privilege escalation or other undefined behavior, but the provided information does not confirm reliable code execution.

If immediate patching is not possible, reduce exposure by limiting local access to untrusted users and restricting the ability to exercise affected IPv6 networking paths. Where operationally feasible, minimize or disable unnecessary IPv6 functionality on systems that do not require it. These measures are only temporary risk reductions; full mitigation requires installing a fixed kernel.

Update the Linux kernel to a version that includes the fix for CVE-2025-40135, specifically the change to use RCU in ip6_xmit() and dst_dev_rcu() for safe destination device access. Vendor kernel updates have been released across multiple supported Red Hat Enterprise Linux and SUSE product lines; apply the relevant vendor-provided kernel package update and reboot the system for the fix to take effect.