CVE-2025-39744 Affecting kernel-uek package, versions <0:6.12.0-104.43.4.2.el9uek


Severity

Recommended
high

Based on Oracle Linux security rating.

Threat Intelligence

EPSS
0.03% (6th percentile)

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  • Snyk IDSNYK-ORACLE9-KERNELUEK-13569148
  • published16 Oct 2025
  • disclosed11 Sept 2025

Introduced: 11 Sep 2025

CVE-2025-39744  (opens in a new tab)

How to fix?

Upgrade Oracle:9 kernel-uek to version 0:6.12.0-104.43.4.2.el9uek or higher.
This issue was patched in ELSA-2025-20662.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-uek package and not the kernel-uek package as distributed by Oracle. See How to fix? for Oracle:9 relevant fixed versions and status.

In the Linux kernel, the following vulnerability has been resolved:

rcu: Fix rcu_read_unlock() deadloop due to IRQ work

During rcu_read_unlock_special(), if this happens during irq_exit(), we can lockup if an IPI is issued. This is because the IPI itself triggers the irq_exit() path causing a recursive lock up.

This is precisely what Xiongfeng found when invoking a BPF program on the trace_tick_stop() tracepoint As shown in the trace below. Fix by managing the irq_work state correctly.

irq_exit() __irq_exit_rcu() /* in_hardirq() returns false after this / preempt_count_sub(HARDIRQ_OFFSET) tick_irq_exit() tick_nohz_irq_exit() tick_nohz_stop_sched_tick() trace_tick_stop() / a bpf prog is hooked on this trace point / __bpf_trace_tick_stop() bpf_trace_run2() rcu_read_unlock_special() / will send a IPI to itself */ irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);

A simple reproducer can also be obtained by doing the following in tick_irq_exit(). It will hang on boot without the patch:

static inline void tick_irq_exit(void) { + rcu_read_lock(); + WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true); + rcu_read_unlock(); +

[neeraj: Apply Frederic's suggested fix for PREEMPT_RT]

CVSS Base Scores

version 3.1