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CVE Record

CVE-2026-43438: sched_ext: Remove redundant css_put() in scx_cgroup_init()

In the Linux kernel, the following vulnerability has been resolved: sched_ext: Remove redundant css_put() in scx_cgroup_init() The iterator css_for_each_descendant_pre() walks the cgroup hierarchy under cgroup_lock(). It does not increment the reference counts on yielded css structs. According to the cgroup documentation, css_put() should only be used to release a reference obtained via css_get() or css_tryget_online(). Since the iterator does not use either of these to acquire a reference, calling css_put() in the error path of scx_cgroup_init() causes a refcount underflow. Remove the unbalanced css_put() to prevent a potential Use-After-Free (UAF) vulnerability.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel reference-counting mistake can underflow an internal cgroup object’s reference count, potentially causing use-after-free. A low-privileged local user may be able to trigger serious confidentiality, integrity, or availability impact. This is a local vulnerability, not an unauthenticated network attack.

Executive priority

Treat this as high-priority kernel maintenance for systems exposed to low-privileged local users. Accelerate remediation on shared and multi-user hosts. Current evidence does not support classifying it as an active, internet-wide emergency.

Technical view

During scx_cgroup_init(), css_for_each_descendant_pre() returns cgroup subsystem-state objects without acquiring references. The error path nevertheless calls css_put(), producing an unbalanced decrement. This can underflow the reference count and potentially free an object while it remains usable, creating a use-after-free condition.

Likely exposure

The record lists Linux kernel versions 6.12, 6.12.78, 6.18.19, 6.19.9, and 7.0 as affected, alongside an ambiguous “0” entry. Actual distribution exposure depends on kernel packaging and backports. Risk is most relevant where low-privileged users have local access.

Exploitation context

The CVSS vector describes local, low-complexity exploitation requiring low privileges and no user interaction, with potentially high confidentiality, integrity, and availability impact. The CVE is not listed as KEV, and the supplied sources provide no evidence of active exploitation or a public exploit.

Researcher notes

The faulty release occurs in scx_cgroup_init() error handling while traversing cgroup descendants under cgroup_lock(). The bundle does not document triggering prerequisites, affected configurations, exploit reliability, or observed attacks. Its version representation is incomplete or ambiguous, so distribution package advisories should govern final exposure decisions.

Mitigation direction

  • Check the operating-system vendor’s advisory for the fixed kernel package applicable to each distribution.
  • Upgrade affected systems to a vendor-supported kernel incorporating the applicable linked stable fix.
  • Prioritize shared or multi-user systems where untrusted users have local accounts.

Validation and detection

  • Inventory running kernel versions and compare them with distribution-specific CVE or package status.
  • Verify the kernel source or package includes removal of the unbalanced css_put() in scx_cgroup_init().
  • After maintenance, confirm every targeted system is running the updated kernel.
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

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CVE-2026-43438 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
0ADP providers
5Source links

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:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2026-43438Attack 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.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux8195136669661fdfe54e9a8923c33b31c92fc1da, 8195136669661fdfe54e9a8923c33b31c92fc1da, 8195136669661fdfe54e9a8923c33b31c92fc1da, 8195136669661fdfe54e9a8923c33b31c92fc1daunaffected
LinuxLinux6.12, 0, 6.12.78, 6.18.19, 6.19.9, 7.0affected
Weakness

CWE details

No CWE listed

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