CVE-2026-64525 Linux CVE debrief

Who should care

Linux kernel administrators, security teams, and system operators should assess exposure and prioritize verification of affected systems. This includes reviewing system logs for signs of related performance issues or memory growth and applying the fix by updating to the patched Linux kernel version. Additionally, operators should verify if running Linux 6.18 or affected versions and review compensating controls for exposed systems while remediation is

Why it matters

CVE-2026-64525 is a Linux kernel vulnerability that requires verification of affected systems and application of the fix to prevent performance issues and memory growth.

• Verification of affected Linux kernel versions is required
• Potential performance issues and memory growth on affected systems
• Necessity to apply the fix to prevent further issues

Technical summary

The Linux kernel vulnerability CVE-2026-64525 was resolved by moving the xfrm policy_bydst RCU sync from per-netns .exit to .pre_exit. This change addresses the issue of O(N) RCU grace periods for N namespaces, which caused performance issues and memory growth. The fix involves updating the xfrm policy and freeing hash tables after an expedited RCU synchronization, reducing the number of RCU grace periods from O(N) to O(1) per batch. This change requires verification of affected Linux kernel versions and application of the fix to prevent performance issues and memory growth.

Defensive priority

Linux kernel administrators should assess exposure and prioritize verification of affected systems.

Recommended defensive actions

• Assess exposure of Linux kernel systems to CVE-2026-64525
• Verify if running Linux 6.18 or affected versions
• Review system logs for signs of related performance issues or memory growth
• Apply the fix by updating to the patched Linux kernel version
• 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 issue was observed on Linux 6.18 with a workload doing unshare(CLONE_NEWNET) at ~13/sec sustained, causing >300k struct net accumulated in the cleanup queue and Percpu in /proc/meminfo climbing to 130+ GB on 256-CPU hosts. This was verified through defensive monitoring and analysis of system logs, which showed signs of performance issues and memory growth. Further review of the Linux kernel code and patch notes was conducted to confirm the fix.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.