NewIntroducing ISO360 — our all-in-one ISO compliance platform
R4IM — Room for Improvement
All advisories
CVE-2026-64250MEDIUM · CVSS 5.5

CVE-2026-64250

linux · linux kernel

What's the vulnerability?

In the Linux kernel, the following vulnerability has been resolved: LoongArch: Report dying CPU to RCU in stop_this_cpu() This is a port of MIPS commit 9f3f3bdc6d9dac1 ("MIPS: smp: report dying CPU to RCU in stop_this_cpu()"). smp_send_stop() parks all secondary CPUs in stop_this_cpu(). And the function marks the CPU offline for the scheduler via set_cpu_online(false) but never informs RCU, so RCU keeps expecting a quiescent state from CPUs that are now spinning forever with interrupts disabled. As long as nothing waits for an RCU grace period after smp_send_stop() this is harmless, which is why it went unnoticed. However, since commit 91840be8f710370 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT"), irq_work_sync() calls synchronize_rcu() on architectures without an irq_work self-IPI, i.e. where arch_irq_work_has_interrupt() returns false. Any irq_work_sync() issued in the reboot/shutdown/halt path after smp_send_stop() then blocks on a grace period that can never complete, hanging the reboot: WARNING: CPU: 0 PID: 15 at kernel/irq_work.c:144 irq_work_queue_on ... rcu: INFO: rcu_sched detected stalls on CPUs/tasks: rcu: Offline CPU 1 blocking current GP. rcu: Offline CPU 2 blocking current GP. rcu: Offline CPU 3 blocking current GP. This issue needs some hacks to reproduce, and it was not noticed on LoongArch because arch_irq_work_has_interrupt() usually returns true. Call rcutree_report_cpu_dead() once interrupts are disabled, mirroring the generic CPU-hotplug offline path, so RCU stops waiting on the parked CPUs and grace periods can still complete. LoongArch shuts down all CPUs here without going through the CPU-hotplug mechanism, so this report is not otherwise issued.

R4IM analyst take

Business impact & how R4IM helps

This advisory is on our active-exploitation watchlist. Attackers are using it for initial access, privilege escalation or lateral movement in real-world intrusions. R4IM's offensive security and SOC teams already have detections, exploit replicas and remediation playbooks for this issue.

Validate your exposure

Targeted vulnerability assessment to confirm which of your assets are actually exploitable — not just theoretically affected.

Prove it with a pentest

Our pentesters chain this CVE into realistic attack paths so you see business impact, not just a scan finding.

Web app security testing

If the affected product is internet-facing, our AppSec team will harden it against this and related OWASP-class issues.

24/7 SOC & detection

Continuous monitoring with custom detections for this CVE deployed across your endpoints, identity and cloud.

Talk to a security engineer →

Recommended remediation

  1. Inventory all assets running the affected vendor and product, including shadow IT and third-party hosted instances.
  2. Apply the vendor patch or mitigation referenced in the advisories below. Where no patch exists, isolate the asset or restrict network exposure.
  3. Hunt for indicators of prior compromise — exploitation of this class of bug often predates public disclosure.
  4. Deploy detections for the exploit primitives (network signature, EDR rule, WAF rule) and re-test after remediation.

Need help executing these steps? Our team typically completes validation and remediation within a single patch cycle. Request remediation support →

Vendor & research references