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CVE Record

CVE-2026-23225: sched/mmcid: Don't assume CID is CPU owned on mode switch

In the Linux kernel, the following vulnerability has been resolved: sched/mmcid: Don't assume CID is CPU owned on mode switch Shinichiro reported a KASAN UAF, which is actually an out of bounds access in the MMCID management code. CPU0 CPU1 T1 runs in userspace T0: fork(T4) -> Switch to per CPU CID mode fixup() set MM_CID_TRANSIT on T1/CPU1 T4 exit() T3 exit() T2 exit() T1 exit() switch to per task mode ---> Out of bounds access. As T1 has not scheduled after T0 set the TRANSIT bit, it exits with the TRANSIT bit set. sched_mm_cid_remove_user() clears the TRANSIT bit in the task and drops the CID, but it does not touch the per CPU storage. That's functionally correct because a CID is only owned by the CPU when the ONCPU bit is set, which is mutually exclusive with the TRANSIT flag. Now sched_mm_cid_exit() assumes that the CID is CPU owned because the prior mode was per CPU. It invokes mm_drop_cid_on_cpu() which clears the not set ONCPU bit and then invokes clear_bit() with an insanely large bit number because TRANSIT is set (bit 29). Prevent that by actually validating that the CID is CPU owned in mm_drop_cid_on_cpu().

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel memory-safety flaw in scheduler MMCID handling. A low-privileged local user could potentially trigger kernel memory corruption, affecting confidentiality, integrity, and availability. The issue is high severity, but the provided sources do not show active exploitation.

Executive priority

Treat as high priority for Linux fleets with local users, shared compute, or untrusted workloads. Patch through normal kernel update channels promptly, but do not assume internet-facing remote exploitation from the provided evidence.

Technical view

The bug occurs during MMCID mode switching when TRANSIT is set but ONCPU is not. sched_mm_cid_exit() incorrectly assumes CPU ownership and calls mm_drop_cid_on_cpu(), leading to an out-of-bounds bit operation. The fix validates CPU ownership before dropping the CID.

Likely exposure

Exposure is limited to systems running affected Linux kernel versions identified in the CVE data. Risk is highest on shared Linux systems or hosts where untrusted local users or workloads can execute code.

Exploitation context

The CVSS vector is local, low complexity, low privilege, and no user interaction. CISA KEV status is false in the bundle, and no cited source claims active exploitation.

Researcher notes

The source describes a KASAN-reported out-of-bounds access related to MMCID TRANSIT and ONCPU state handling. Affected-version evidence in the bundle is limited and should be cross-checked against vendor kernel branches and the two upstream stable commits.

Mitigation direction

  • Check Linux vendor or distribution advisories for patched kernel packages.
  • Apply kernel updates containing the referenced stable fixes.
  • Prioritize shared systems and hosts running untrusted workloads.
  • Restrict untrusted local shell or workload access where patching is delayed.

Validation and detection

  • Inventory running Linux kernel versions across affected environments.
  • Compare kernel versions against CVE and vendor advisory affected ranges.
  • Confirm whether referenced stable commits are present in deployed kernels.
  • Track CISA KEV and vendor advisories for exploitation or mitigation updates.
Prepared
Confidence
medium
Sources
4

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-2026-23225 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
3Source 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-2026-23225Attack 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
LinuxLinux007d84287c7466ca68a5809b616338214dc5b77b, 007d84287c7466ca68a5809b616338214dc5b77bunaffected
LinuxLinux6.19, 0, 6.19.1, 7.0affected
Weakness

CWE details

No CWE listed

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