CVE-2026-64188 Linux CVE debrief

Who should care

Linux kernel developers and users, network administrators, and security professionals should be aware of this vulnerability. They should assess their exposure, apply patches or mitigations, and monitor for suspicious activity on the network. Additionally, Linux distribution maintainers and security teams should prioritize patching or mitigating this vulnerability to prevent potential exploitation.

Technical summary

The vulnerability is caused by the rmnet_dellink() function removing an endpoint from the hash table with hlist_del_init_rcu() and then immediately freeing it with kfree(). However, RCU readers on the receive path (rmnet_rx_handler -> __rmnet_map_ingress_handler) may still hold a reference to the endpoint and dereference ep->egress_dev after the memory has been freed. The endpoint is a kmalloc-32 object, and the stale read at offset 8 corresponds to the egress_dev pointer. The fix adds an rcu_head field to struct rmnet_endpoint and replaces kfree() with kfree_rcu() to ensure the endpoint memory remains valid through the RCU grace period.

Defensive priority

High

Recommended defensive actions

• Update the Linux kernel to a version that includes the fix
• Use a Linux distribution that has backported the fix
• Disable the rmnet module if it is not needed
• Monitor for suspicious activity on the network
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The vulnerability was discovered in the Linux kernel's rmnet module. The fix involves adding an rcu_head field to struct rmnet_endpoint and replacing kfree() with kfree_rcu() so the endpoint memory remains valid through the RCU grace period. The CVE record was published on 2026-07-20T17:18:21.853Z and has not been modified since then. The vulnerability has a CVSS score of 7.8 and is considered HIGH severity.

Official resources