CVE-2025-21767 — clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context
In the Linux kernel, the following vulnerability has been resolved: clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context The following bug report happened with a PREEMPT_RT kernel: BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2012, name: kwatchdog preempt_count: 1, expected: 0 RCU nest depth: 0, expected: 0 get_random_u32+0x4f/0x110 clocksource_verify_choose_cpus+0xab/0x1a0 clocksource_verify_percpu.part.0+0x6b/0x330 clocksource_watchdog_kthread+0x193/0x1a0 It is due to the fact that clocksource_verify_choose_cpus() is invoked with preemption disabled. This function invokes get_random_u32() to obtain random numbers for choosing CPUs. The batched_entropy_32 local lock and/or the base_crng.lock spinlock in driver/char/random.c will be acquired during the call. In PREEMPT_RT kernel, they are both sleeping locks and so cannot be acquired in atomic context. Fix this problem by using migrate_disable() to allow smp_processor_id() to be reliably used without introducing atomic context. preempt_disable() is then called after clocksource_verify_choose_cpus() but before the clocksource measurement is being run to avoid introducing unexpected latency.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+1
- Technical severity (medium)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Linux | Linux |
≥ 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and < 852805b6cbdb69c298a8fc9fbe79994c95106e04version 5.14≥ 5.13.2 and < 5.14≥ 5.12.17 and < 5.13≥ 5.10.50 and < 5.10.235version 155d3c5d24ee13cafa6236b49fc02b240a511d59version 193e14e68e907b2a7a936a7726accbaa4df25a4d≥ 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and < 6bb05a33337b2c842373857b63de5c9bf1ae2a09 and 5 more≥ 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and < 0fb534187d2355f6c8f995321e76d1ccd1262ac1≥ 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and < cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa≥ 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and < 8783ceeee797d9aa9cfe150690fb9d0bac8cc459≥ 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and < 60f54f0d4ea530950549a8263e6fdd70a40490a4≥ d9b40ebd448e437ffbc65f013836f98252279a82 and < d9c217fadfcff7a8df58567517d1e4253f3fd243 |
Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel | ≥ 5.10.50 and < 5.10.235version 6.14-rc1≥ 6.13 and < 6.13.4≥ 6.7 and < 6.12.16≥ 6.2 and < 6.6.79≥ 5.16 and < 6.1.129≥ 5.13.2 and < 5.15.179≥ 5.12.17 and < 5.13 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 5.5 | CVSS 3.1 | Medium | 1.8 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
| 5.5 | CVSS 3.1 | Medium | — | — | GitHub, Inc. via GitHub Security Advisories |
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- Record published
- Fix documented
- Affected products added · linux/linux kernel
- CVSS changed · 5.5
- Source status changed · → Modified
- Record created in this database
- 2025
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
13 on the record
- git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4
- git.kernel.org/stable/c/d9c217fadfcff7a8df58567517d1e4253f3fd243
- git.kernel.org/stable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa
- git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1
- git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09
- git.kernel.org/stable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459
- git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04
- cert-portal.siemens.com/productcert/html/ssa-082556.html
- lists.debian.org/debian-lts-announce/2025/05/msg00030.html
- nvd.nist.gov/vuln/detail/CVE-2025-21767
- cert-portal.siemens.com/productcert/html/ssa-784472.html
- github.com/advisories/GHSA-h97w-34cr-4pxx
- lists.debian.org/debian-lts-announce/2025/03/msg00028.html
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 7h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 7h
- Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
- Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
- Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CISA SSVC assessment.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2025-21767 is "clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context", rated Medium. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.5 describes technical severity. EPSS 0.18% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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