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CVE Record

CVE-2025-21995: drm/sched: Fix fence reference count leak

In the Linux kernel, the following vulnerability has been resolved: drm/sched: Fix fence reference count leak The last_scheduled fence leaks when an entity is being killed and adding the cleanup callback fails. Decrement the reference count of prev when dma_fence_add_callback() fails, ensuring proper balance. [phasta: add git tag info for stable kernel]

MediumCVSS 5.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2025-21995 is a Linux kernel denial-of-service issue in the DRM scheduler. A local authenticated user could trigger a fence reference count leak that may exhaust resources and affect availability. It is not described as data theft or privilege escalation.

Executive priority

Treat as a routine but real availability fix. It should be included in normal kernel patch cycles, with higher urgency for shared Linux systems or workstations where untrusted local users have access.

Technical view

The bug is in drm/sched cleanup handling. When an entity is killed and dma_fence_add_callback() fails, last_scheduled can leak because the previous fence reference is not decremented. The fix balances the reference count. CVSS is 5.5, local attack vector, low complexity, low privileges, no user interaction, high availability impact.

Likely exposure

Exposure is most relevant on Linux systems running affected kernel versions with DRM scheduler code. The CVE record lists Linux kernel versions including 6.2, 6.6.85, 6.12.21, 6.13.9, and 6.14 as affected markers. Distribution backports may change practical exposure.

Exploitation context

The source bundle does not cite active exploitation, and the CVE is not marked in KEV. The CVSS vector requires local access and low privileges. Available evidence supports availability risk, not remote compromise or confidentiality impact.

Researcher notes

The public record identifies a reference-count leak and stable kernel fixes, but does not provide a CWE, exploit evidence, or detailed distribution status. Avoid assuming exposure from upstream versions alone; validate against vendor kernels and backport notes.

Mitigation direction

  • Apply Linux kernel or distribution updates that include the referenced stable fixes.
  • Check vendor advisories for backported fixes before relying on upstream version numbers.
  • Prioritize multi-user Linux systems where local users can exercise GPU or DRM paths.
  • Monitor systems for unusual resource exhaustion until updates are deployed.

Validation and detection

  • Inventory running kernel versions across Linux hosts.
  • Confirm whether distribution kernels contain the referenced stable commits or equivalent backports.
  • Map exposed systems that allow local users access to DRM or GPU functionality.
  • Review vendor security advisories for CVE-2025-21995 remediation status.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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

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CVE-2025-21995 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

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.

1CVSS vectors
3Timeline events
1ADP providers
5Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2025-21995Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux2fdb8a8f07c2f1353770a324fd19b8114e4329ac, 2fdb8a8f07c2f1353770a324fd19b8114e4329ac, 2fdb8a8f07c2f1353770a324fd19b8114e4329ac, 2fdb8a8f07c2f1353770a324fd19b8114e4329acunaffected
LinuxLinux6.2, 0, 6.6.85, 6.12.21, 6.13.9, 6.14affected
Weakness

CWE details

No CWE listed

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