Security readout for executives and security teams
Plain-English summary
This Linux kernel issue affects the scheduler extension path. The documented impact is a kernel warning caused by using the wrong runqueue lock in a specific bypass routine. Public sources do not show data theft, privilege escalation, or active exploitation.
Executive priority
Treat as routine kernel maintenance unless your environment relies on affected 6.12/6.13 kernels at scale. Prioritize normal patch cycles and vendor confirmation.
Technical view
In sched_ext, scx_ops_bypass() iterates CPUs to re-enqueue scx tasks. It used rq_lock() even for offline CPUs or CPUs running higher scheduler classes, which can trigger a warning in rq_pin_lock(). The fix replaces rq_lock() with raw_spin_rq_lock().
Likely exposure
Exposure appears limited to Linux kernels in the affected 6.12/6.13 range or vendor kernels carrying the vulnerable sched_ext code. Actual exposure depends on distribution backports and kernel configuration.
Exploitation context
No KEV listing is present, and the provided sources do not report active exploitation or a public exploit. The observable issue in the record is a kernel warning during scheduler behavior.
Researcher notes
The CVE record frames this as a resolved Linux kernel correctness issue with an observed warning. Severity, CVSS, and CWE are not provided. Do not infer exploitability beyond the cited scheduler warning without additional evidence.
Mitigation direction
- Update to a vendor-supported kernel containing the referenced stable fixes.
- Check distribution advisories for backported fixes before relying on upstream version numbers.
- If no vendor fix is available, monitor vendor guidance and assess sched_ext usage exposure.
Validation and detection
- Inventory Linux kernel versions across affected systems.
- Check vendor changelogs for the referenced kernel commits.
- Review kernel logs for the warning string shown in the CVE record.
- Confirm whether deployed kernels include sched_ext code paths.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2025-21657 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
Source materials
- CVE List V5 sourceCVE List V5
- https://git.kernel.org/stable/c/d9e446dd63cee7161717a6a8414ba9c6435af764CVE reference, Linux
- https://git.kernel.org/stable/c/6268d5bc10354fc2ab8d44a0cd3b042d49a0417eCVE reference, Linux
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.