CVE-2025-21816

MEDIUMNVD 5.55.5—
EchelonGraph scoreMEDIUM confidence

Score 5.5 from GitHub Security Advisory published 2025-02-27. NVD baseline CVSS 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.5Exploit: None knownExposed: 0

A fix is available — apply it.

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 <- stop_machine_cpuslocked+0x66/0xc0 RIP: 0010:hrtimer_start_range_ns+0x289/0x2d0 Call Trace: 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.

CVSS v3
5.5
EG Score
5.5(medium)
EG Risk
29(Track)
EG Risk 29/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity55% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
10%
KEV
Not listed

Published

February 27, 2025

Last Modified

November 3, 2025

References (6)

Vendor Advisories for CVE-2025-21816(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(13)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-tools-aws (6.11.0-1014.15) @ oracular2026-05-30ubuntu
ubuntulinux-tools-oracle-64k (6.11.0-1016.17) @ oracular2026-05-30ubuntu
ubuntulinux-virtual-6.8 (6.8.0-64.67) @ noble2026-05-30ubuntu
ubuntulinux-virtual-hwe-24.04-edge (6.11.0-26.26~24.04.1) @ noble2026-05-30ubuntu
ubuntulinux-tools-realtime-6.8.1 (6.8.1-1025.26) @ noble2026-05-30ubuntu
ubuntulinux-virtual-hwe-22.04-edge (6.8.0-64.67~22.04.1) @ jammy2026-05-30ubuntu
ubuntulinux-tools-lowlatency-hwe-22.04-edge (6.8.0-64.67.1~22.04.1) @ jammy2026-05-30ubuntu
ubuntulinux-tools-oracle-lts-24.04 (6.8.0-1029.30) @ noble2026-05-30ubuntu
ubuntulinux-tools-gcp-lts-24.04 (6.8.0-1033.35) @ noble2026-05-30ubuntu
ubuntulinux-tools-raspi-6.8 (6.8.0-1031.35) @ noble2026-05-30ubuntu
ubuntulinux-tools-raspi-realtime-6.8 (6.8.0-2026.27) @ noble2026-05-30ubuntu
ubuntulinux-tools-azure-nvidia-lts-24.04 (6.8.0-1022.23) @ noble2026-05-30ubuntu
linuxKernel @ 6.1.141—osv

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

All Vendor Advisories

(12)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 7× in last 7d / 40× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 108 total refreshes for this CVE.

  1. 2026-08-07 16:26 UTCEPSS rescore
  2. 2026-08-06 13:46 UTCEPSS rescore
  3. 2026-08-05 19:16 UTCEPSS rescore
  4. 2026-08-04 15:09 UTCEPSS rescore
  5. 2026-08-04 10:37 UTCEPSS rescore
  6. 2026-08-03 10:35 UTCEPSS rescore
  7. 2026-08-02 02:25 UTCEPSS rescore
  8. 2026-08-01 04:15 UTCEPSS rescore
  9. 2026-07-30 16:27 UTCEPSS rescore
  10. 2026-07-30 01:29 UTCEPSS rescore
  11. 2026-07-28 15:35 UTCEPSS rescore
  12. 2026-07-27 14:12 UTCEPSS rescore
  13. 2026-07-26 14:53 UTCEPSS rescore
  14. 2026-07-25 14:17 UTCEPSS rescore
  15. 2026-07-24 14:17 UTCEPSS rescore
  16. 2026-07-24 13:41 UTCOSV refresh
  17. 2026-07-23 14:17 UTCEPSS rescore
  18. 2026-07-23 02:50 UTCEG score recompute
  19. 2026-07-22 14:07 UTCEPSS rescore
  20. 2026-07-22 14:07 UTCEPSS rescore
  21. 2026-07-21 15:24 UTCEPSS rescore
  22. 2026-07-20 17:07 UTCEPSS rescore
  23. 2026-07-19 14:30 UTCEPSS rescore
  24. 2026-07-19 14:30 UTCEPSS rescore
  25. 2026-07-19 02:28 UTCEPSS rescore
Show 75 more
  1. 2026-07-19 02:28 UTCEPSS rescore
  2. 2026-07-18 10:03 UTCEPSS rescore
  3. 2026-07-16 17:02 UTCEPSS rescore
  4. 2026-07-15 16:57 UTCEPSS rescore
  5. 2026-07-15 16:57 UTCEPSS rescore
  6. 2026-07-15 01:59 UTCEPSS rescore
  7. 2026-07-13 22:29 UTCEPSS rescore
  8. 2026-07-13 22:29 UTCEPSS rescore
  9. 2026-07-13 06:12 UTCEPSS rescore
  10. 2026-07-13 06:12 UTCEPSS rescore
  11. 2026-07-12 05:46 UTCEPSS rescore
  12. 2026-07-12 05:46 UTCEPSS rescore
  13. 2026-07-11 08:27 UTCEPSS rescore
  14. 2026-07-11 08:26 UTCEPSS rescore
  15. 2026-07-09 19:09 UTCEPSS rescore
  16. 2026-07-08 15:14 UTCEPSS rescore
  17. 2026-07-07 13:45 UTCEPSS rescore
  18. 2026-07-07 08:51 UTCOSV refresh
  19. 2026-07-06 16:26 UTCEPSS rescore
  20. 2026-07-06 02:22 UTCEPSS rescore
  21. 2026-07-06 02:22 UTCEPSS rescore
  22. 2026-07-05 02:30 UTCEPSS rescore
  23. 2026-07-04 06:30 UTCEPSS rescore
  24. 2026-07-01 15:06 UTCEPSS rescore
  25. 2026-06-29 14:06 UTCEPSS rescore
  26. 2026-06-28 14:07 UTCEPSS rescore
  27. 2026-06-28 14:07 UTCEPSS rescore
  28. 2026-06-28 04:55 UTCEPSS rescore
  29. 2026-06-28 04:55 UTCEPSS rescore
  30. 2026-06-27 03:08 UTCEPSS rescore
  31. 2026-06-27 03:08 UTCEPSS rescore
  32. 2026-06-25 13:49 UTCEPSS rescore
  33. 2026-06-25 13:49 UTCEPSS rescore
  34. 2026-06-24 14:04 UTCEPSS rescore
  35. 2026-06-24 14:04 UTCEPSS rescore
  36. 2026-06-23 21:32 UTCEPSS rescore
  37. 2026-06-23 21:32 UTCEPSS rescore
  38. 2026-06-22 14:25 UTCEPSS rescore
  39. 2026-06-22 14:25 UTCEPSS rescore
  40. 2026-06-21 14:56 UTCEPSS rescore
  41. 2026-06-21 14:56 UTCEPSS rescore
  42. 2026-06-21 01:59 UTCEPSS rescore
  43. 2026-06-21 01:59 UTCEPSS rescore
  44. 2026-06-19 19:25 UTCEPSS rescore
  45. 2026-06-19 19:25 UTCEPSS rescore
  46. 2026-06-18 20:05 UTCOSV refresh
  47. 2026-06-18 17:52 UTCEPSS rescore
  48. 2026-06-18 17:52 UTCEPSS rescore
  49. 2026-06-17 17:52 UTCEPSS rescore
  50. 2026-06-16 17:52 UTCEPSS rescore
  51. 2026-06-16 17:52 UTCEPSS rescore
  52. 2026-06-15 17:48 UTCEPSS rescore
  53. 2026-06-14 23:17 UTCEPSS rescore
  54. 2026-06-13 22:59 UTCEPSS rescore
  55. 2026-06-12 23:11 UTCEPSS rescore
  56. 2026-06-11 13:59 UTCEPSS rescore
  57. 2026-06-10 22:18 UTCEPSS rescore
  58. 2026-06-10 13:22 UTCEPSS rescore
  59. 2026-06-08 14:16 UTCEPSS rescore
  60. 2026-06-08 14:16 UTCEPSS rescore
  61. 2026-06-07 15:24 UTCEPSS rescore
  62. 2026-06-07 15:24 UTCEPSS rescore
  63. 2026-06-06 13:47 UTCEPSS rescore
  64. 2026-06-06 13:47 UTCEPSS rescore
  65. 2026-06-05 22:46 UTCEPSS rescore
  66. 2026-06-05 22:46 UTCEPSS rescore
  67. 2026-06-05 06:10 UTCEPSS rescore
  68. 2026-06-05 06:10 UTCEPSS rescore
  69. 2026-06-04 13:11 UTCEPSS rescore
  70. 2026-06-04 13:11 UTCEPSS rescore
  71. 2026-06-02 20:12 UTCEPSS rescore
  72. 2026-06-02 20:12 UTCEPSS rescore
  73. 2026-06-01 13:51 UTCEPSS rescore
  74. 2026-06-01 13:51 UTCEPSS rescore
  75. 2026-05-31 22:30 UTCEPSS rescore

Related CVEs(same product + same vendor)

Frequently asked(5)

What is CVE-2025-21816?
CVE-2025-21816 is a medium vulnerability published on February 27, 2025. In the Linux kernel, the following vulnerability has been resolved: hrtimers: Force migrate away hrtimers queued after CPUHPAPHRTIMERS_DYING hrtimers are migrated away from the dying CPU to any online target at the CPUHPAPHRTIMERS_DYING stage in order not to delay bandwidth timers handling tasks…
When was CVE-2025-21816 disclosed?
CVE-2025-21816 was first published in the National Vulnerability Database on February 27, 2025, with the most recent update on November 3, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2025-21816 actively exploited?
CVE-2025-21816 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 89.9% of all scored CVEs.
What is the CVSS score of CVE-2025-21816?
CVE-2025-21816 has a CVSS v3 base score of 5.5 (NVD).
How do I remediate CVE-2025-21816?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2025-21816, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2025-21816

Explore →

Is Your Infrastructure Affected by CVE-2025-21816?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs