cbcvebase.
CVE-2025-21816
published 2025-02-27

CVE-2025-21816: In the Linux kernel, the following vulnerability has been resolved: hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING hrtimers are…

PriorityP420medium5.5CVSS 3.1
AVLACLPRLUINSUCNINAH
EPSS
0.20%
10.2th percentile
In the Linux kernel, the following vulnerability has been resolved: hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING hrtimers are migrated away from the dying CPU to any online target at the CPUHP_AP_HRTIMERS_DYING stage in order not to delay bandwidth timers handling tasks involved in the CPU hotplug forward progress. However wakeups can still be performed by the outgoing CPU after CPUHP_AP_HRTIMERS_DYING. Those can result again in bandwidth timers being armed. Depending on several considerations (crystal ball power management based election, earliest timer already enqueued, timer migration enabled or not), the target may eventually be the current CPU even if offline. If that happens, the timer is eventually ignored. The most notable example is RCU which had to deal with each and every of those wake-ups by deferring them to an online CPU, along with related workarounds: _ e787644caf76 (rcu: Defer RCU kthreads wakeup when CPU is dying) _ 9139f93209d1 (rcu/nocb: Fix RT throttling hrtimer armed from offline CPU) _ f7345ccc62a4 (rcu/nocb: Fix rcuog wake-up from offline softirq) The problem isn't confined to RCU though as the stop machine kthread (which runs CPUHP_AP_HRTIMERS_DYING) reports its completion at the end of its work through cpu_stop_signal_done() and performs a wake up that eventually arms the deadline server timer: WARNING: CPU: 94 PID: 588 at kernel/time/hrtimer.c:1086 hrtimer_start_range_ns+0x289/0x2d0 CPU: 94 UID: 0 PID: 588 Comm: migration/94 Not tainted Stopper: multi_cpu_stop+0x0/0x120 start_dl_timer enqueue_dl_entity dl_server_start enqueue_task_fair enqueue_task ttwu_do_activate try_to_wake_up complete cpu_stopper_thread Instead of providing yet another bandaid to work around the situation, fix it in the hrtimers infrastructure instead: always migrate away a timer to an online target whenever it is enqueued from an offline CPU. This will also allow to revert all the above RCU disgraceful hacks.

Affected

35 ranges· showing 25
VendorProductVersion rangeFixed in
debianlinux< linux 6.1.147-1 (bookworm)linux 6.1.147-1 (bookworm)
debianlinux-6.1< linux 6.1.147-1 (bookworm)linux 6.1.147-1 (bookworm)
linuxlinux
linuxlinux
linuxlinux
linuxlinux
linuxlinux
linuxlinux>= 4.19.302 < 4.204.20
linuxlinux>= 5.10.204 < 5.115.11
linuxlinux>= 5.15.143 < 5.165.16
linuxlinux>= 5.4.264 < 5.55.5
linuxlinux>= 53f408cad05bb987af860af22f4151e5a18e6ee8 < 63815bef47ec25f5a125019ca480882481ee155363815bef47ec25f5a125019ca480882481ee1553
linuxlinux>= 5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 < e456a88bddae4030ba962447bb84be6669f2a0c1e456a88bddae4030ba962447bb84be6669f2a0c1
linuxlinux>= 5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 < 2aecec58e9040ce3d2694707889f9914a23749552aecec58e9040ce3d2694707889f9914a2374955
linuxlinux>= 5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 < 53dac345395c0d2493cbc2f4c85fe38aef5b63f553dac345395c0d2493cbc2f4c85fe38aef5b63f5
linuxlinux>= 6.1.68 < 6.1.1416.1.141
linuxlinux>= 6.6.7 < 6.6.936.6.93
linuxlinux>= 75b5016ce325f1ef9c63e5398a1064cf8a7a7354 < 82ac6adbbb2aad14548a71d5e2e37f4964a15e3882ac6adbbb2aad14548a71d5e2e37f4964a15e38
linuxlinux_kernel
linuxlinux_kernel
linuxlinux_kernel>= 0 < 6.1.147-16.1.147-1
linuxlinux_kernel>= 0 < 6.12.15-16.12.15-1
linuxlinux_kernel>= 0 < 6.12.15-16.12.15-1
linuxlinux_kernel>= 0 < 6.8.0-64.676.8.0-64.67
linuxlinux_kernel>= 4.19.302 < 4.204.20

CVSS provenance

nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
osv7.8HIGH
vendor_ubuntu7.8HIGH
vendor_debian5.5MEDIUM
vendor_msrc5.5MEDIUM
vendor_redhat5.5MEDIUM
Stop checking back — get the weekly exploitation signal.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.