Linux Kernel: security vulnerability (CVE-2025-21767)
Published Last modified Sources: Siemens ProductCERT, BSI, SUSE, Debian LTS, CVE.org, EUVD
What is affected, what to do
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 available sources name no fixed version. Check the vendor guidance in the references below.
Conflicting version data — version display is hidden until the data is resolved.
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Metrics
5.5
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
5.5
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: Siemens ProductCERT, BSI, SUSE, Debian LTS, CVE.org, EUVD
0.2 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 7.4
Show all metrics
- Severity
- Medium
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 35.94 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 5.5 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 5.5
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.2 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 7.4
- Low — this CVE sits in the lower 10% of all CVEs scored today.
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
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.
Source: siemens_advisory, BSI CSAF, BSI WID Portal, suse_csaf, Debian LTS Advisories, cvelistv5, NVD (NIST), CVE.org (MITRE), ENISA EUVD
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| Linux | Linux |
|
|
| Dell | Secure Connect Gateway |
|
|
| Siemens | SIMATIC S7 |
|
|
Vendors and products
Affected operating systems
| Linux | debian | linux | bullseye |
| Linux | debian | linux-6.1 | bullseye |
| Linux | linux | linux_kernel | 6.14 |
| Linux | linux | linux_kernel | — |
References & sources
- git.kernel.orgstable/c/d9c217fadfcff7a8df58567517d1e4253f3fd243
- git.kernel.orgstable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4
- git.kernel.orgstable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04
- git.kernel.orgstable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459
- git.kernel.orgstable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa
- git.kernel.orgstable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1
- git.kernel.orgstable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09
- lists.debian.orgdebian-lts-announce/2025/05/msg00030.html
- lists.debian.orgdebian-lts-announce/2025/03/msg00028.html
- Siemens ProductCERTproductcert/html/ssa-082556.html
- Siemens ProductCERTproductcert/html/ssa-784472.html
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedLinux
New references:- https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1
- https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4
- https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09
- https://git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04
and 3 more references
Show 21 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1Reference added —https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4Reference added —https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09Reference added —https://git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04Reference added —https://git.kernel.org/stable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459Reference added —https://git.kernel.org/stable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faaReference added —https://git.kernel.org/stable/c/d9c217fadfcff7a8df58567517d1e4253f3fd243Reference removed https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1—Reference removed https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4—Reference removed https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09—Reference removed https://git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04—Reference removed https://git.kernel.org/stable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459—Reference removed https://git.kernel.org/stable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa—Reference removed https://git.kernel.org/stable/c/d9c217fadfcff7a8df58567517d1e4253f3fd243—Reference type removed https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1 Types: Patch—Reference type removed https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4 Types: Patch—Reference type removed https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09 Types: Patch—Reference type removed https://git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04 Types: Patch—Reference type removed https://git.kernel.org/stable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459 Types: Patch—Reference type removed https://git.kernel.org/stable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa Types: Patch—Reference type removed https://git.kernel.org/stable/c/d9c217fadfcff7a8df58567517d1e4253f3fd243 Types: Patch—Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Record modifiedCVE Program
Show 4 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://lists.debian.org/debian-lts-announce/2025/03/msg00028.htmlReference added —https://lists.debian.org/debian-lts-announce/2025/05/msg00030.htmlReference removed https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html—Reference removed https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html—Source identifier: af854a3a-2127-422b-91ae-364da2661108
Record modifiedSiemens ADP
Show 4 original changes
Individual changes of this event as published by NVD Type Action Before After Affected versions (publisher) added —Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2025/21xxx/CVE-2025-21767.json">CVE-2025-21767</a>Reference added —https://cert-portal.siemens.com/productcert/html/ssa-082556.htmlReference added —https://cert-portal.siemens.com/productcert/html/ssa-784472.htmlReference removed https://cert-portal.siemens.com/productcert/html/ssa-082556.html—Source identifier: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
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<a href="https://intel.neosec.eu/en/cve/CVE-2025-21767"><img src="https://intel.neosec.eu/badge/cve/CVE-2025-21767.svg?lang=en" alt="CVE-2025-21767 – NEOSEC Intel" height="20"></a>