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CVE Record

CVE-2025-21893: keys: Fix UAF in key_put()

In the Linux kernel, the following vulnerability has been resolved: keys: Fix UAF in key_put() Once a key's reference count has been reduced to 0, the garbage collector thread may destroy it at any time and so key_put() is not allowed to touch the key after that point. The most key_put() is normally allowed to do is to touch key_gc_work as that's a static global variable. However, in an effort to speed up the reclamation of quota, this is now done in key_put() once the key's usage is reduced to 0 - but now the code is looking at the key after the deadline, which is forbidden. Fix this by using a flag to indicate that a key can be gc'd now rather than looking at the key's refcount in the garbage collector.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2025-21893 is a Linux kernel use-after-free in key_put(), part of the kernel key management code. A local low-privileged attacker is the modeled threat. The CVSS impact is high for confidentiality, integrity, and availability, so affected servers and shared Linux hosts should be patched promptly.

Executive priority

Treat as a high-priority local kernel patching issue, especially for shared Linux infrastructure. It is not evidenced as actively exploited in the provided sources, but the impact rating justifies timely remediation through normal emergency or accelerated kernel maintenance processes.

Technical view

The bug occurs after a key reference count reaches zero: garbage collection may destroy the key, but key_put() could still inspect it while reclaiming quota. The upstream fix changes the design to use a garbage-collection flag instead of reading the key refcount after the object may be freed.

Likely exposure

Exposure is Linux systems running affected kernel builds identified by the CVE metadata, including versions around 6.10, 6.12.21, 6.13.9, and 6.14. Distribution backport status must be verified because package versions may not match upstream kernel numbers.

Exploitation context

The CVSS vector is local, low complexity, low privileges, and no user interaction. The provided sources do not show KEV listing or active exploitation. Evidence supports serious local impact potential, but not remote exploitation or known in-the-wild abuse.

Researcher notes

The source bundle gives the root cause and fix direction but not exploitability details, affected distribution packages, or proof-of-concept status. Avoid assuming all 6.x kernels are affected; validate against upstream commits and distribution backports.

Mitigation direction

  • Apply Linux kernel updates from your distribution or vendor when available.
  • Verify updates include the listed stable kernel fixes or CVE backport.
  • Reboot systems after kernel update so the fixed kernel is running.
  • Prioritize multi-user, shared hosting, container, and developer workstation environments.
  • If no vendor advisory exists, monitor official kernel and distribution guidance.

Validation and detection

  • Inventory running kernel versions across Linux assets.
  • Map kernel packages to vendor advisories or upstream stable commits.
  • Confirm the active booted kernel is the patched version after reboot.
  • Check change logs for CVE-2025-21893 or the referenced commit IDs.
  • Review exposure where untrusted local users or workloads can execute code.
Prepared
Confidence
medium
Sources
5

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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cwe · low confidence lookup

CWE-416: Exact CWE lookup

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cve · low confidence lookup

CVE-2025-21893 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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
4Source links

SSVC decision data

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

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
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-21893Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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
LinuxLinux9578e327b2b4935a25d49e3891b8fcca9b6c10c6, 9578e327b2b4935a25d49e3891b8fcca9b6c10c6, 9578e327b2b4935a25d49e3891b8fcca9b6c10c6unaffected
LinuxLinux6.10, 0, 6.12.21, 6.13.9, 6.14affected
Weakness

CWE details

CWE-416

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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