CVE-2025-21840: thermal/netlink: Prevent userspace segmentation fault by adjusting UAPI header
In the Linux kernel, the following vulnerability has been resolved:
thermal/netlink: Prevent userspace segmentation fault by adjusting UAPI header
The intel-lpmd tool [1], which uses the THERMAL_GENL_ATTR_CPU_CAPABILITY
attribute to receive HFI events from kernel space, encounters a
segmentation fault after commit 1773572863c4 ("thermal: netlink: Add the
commands and the events for the thresholds").
The issue arises because the THERMAL_GENL_ATTR_CPU_CAPABILITY raw value
was changed while intel_lpmd still uses the old value.
Although intel_lpmd can be updated to check the THERMAL_GENL_VERSION and
use the appropriate THERMAL_GENL_ATTR_CPU_CAPABILITY value, the commit
itself is questionable.
The commit introduced a new element in the middle of enum thermal_genl_attr,
which affects many existing attributes and introduces potential risks
and unnecessary maintenance burdens for userspace thermal netlink event
users.
Solve the issue by moving the newly introduced
THERMAL_GENL_ATTR_TZ_PREV_TEMP attribute to the end of the
enum thermal_genl_attr. This ensures that all existing thermal generic
netlink attributes remain unaffected.
[ rjw: Subject edits ]
Security readout for executives and security teams
Plain-English summary
This Linux kernel issue can crash userspace thermal-management software because a kernel interface value changed unexpectedly. The cited example is intel-lpmd receiving thermal/HFI events. Sources describe a reliability and compatibility problem, not data theft or remote compromise.
Executive priority
Treat this as a low-priority reliability fix unless your fleet depends on Linux thermal management tooling. Include it in normal kernel patch cycles, with faster attention for laptops, edge systems, or performance-managed hosts using intel-lpmd.
Technical view
A thermal generic netlink UAPI enum was changed by inserting THERMAL_GENL_ATTR_TZ_PREV_TEMP in the middle. Existing attribute numbers shifted, so userspace expecting the old THERMAL_GENL_ATTR_CPU_CAPABILITY value could misinterpret events and segfault. The fix moves the new attribute to the end.
Likely exposure
Exposure appears limited to Linux systems on affected 6.13-era kernels that use thermal generic netlink consumers, especially intel-lpmd/HFI event handling. Systems not using these userspace thermal event paths are less likely to see impact.
Exploitation context
The source bundle does not cite active exploitation, KEV listing, public exploit activity, or remote attack paths. The documented symptom is a userspace segmentation fault triggered by kernel/userspace API incompatibility after a kernel change.
Researcher notes
The evidence supports an ABI compatibility regression in Linux thermal netlink attributes. The CVE record lists no CVSS, CWE, or KEV status. Avoid broad claims beyond userspace crash risk unless vendor advisories add more impact detail.
Mitigation direction
Apply a vendor kernel update containing the referenced stable thermal/netlink fix.
Prioritize systems using intel-lpmd or thermal generic netlink event consumers.
Check distribution advisories before relying on upstream commit hashes alone.
If patching is delayed, review operational impact of affected thermal userspace tooling.
Validation and detection
Inventory systems running affected Linux 6.13 or 6.14 kernel builds.
Confirm whether the stable fix is present in the deployed kernel package.
Identify hosts running intel-lpmd or other thermal generic netlink consumers.
Review crash reports for intel-lpmd segmentation faults after kernel updates.
After patching, verify thermal event consumers remain stable under normal workload.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Potential ATT&CK relevance
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CVE-2025-21840 mapping review
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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.
0CVSS vectors
3Timeline events
0ADP providers
3Source links
Vulnerability timeline
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CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
CVE publishedCVE Program
The CVE record was published.
Mar 7, 2025, 09:09 UTC (UTC+00:00)
CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.