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CVE Record

CVE-2026-23204: net/sched: cls_u32: use skb_header_pointer_careful()

In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: use skb_header_pointer_careful() skb_header_pointer() does not fully validate negative @offset values. Use skb_header_pointer_careful() instead. GangMin Kim provided a report and a repro fooling u32_classify(): BUG: KASAN: slab-out-of-bounds in u32_classify+0x1180/0x11b0 net/sched/cls_u32.c:221

HighCVSS 7.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel traffic-classification flaw can read beyond allocated memory because negative packet offsets were not fully validated. A local attacker with low privileges, as scored, could potentially expose sensitive kernel data or crash the system. The supplied CVSS score is 7.1 (high); no integrity impact is identified.

Executive priority

Prioritize remediation as high, especially for multi-user systems, shared compute, and appliances permitting local low-privilege access. Accelerate patching where sensitive data or service availability is important. Confirm vendor-specific exposure before declaring systems vulnerable because the supplied version mapping is incomplete.

Technical view

The cls_u32 classifier called skb_header_pointer(), which incompletely validates negative offsets. A reported reproducer triggered a KASAN slab-out-of-bounds condition in u32_classify() at net/sched/cls_u32.c:221. Stable fixes replace that call with skb_header_pointer_careful().

Likely exposure

Exposure is most likely on affected Linux kernels where the u32 traffic classifier is reachable. The supplied version data mixes release numbers and commit hashes and does not provide a dependable branch-by-branch range. Confirm exposure using distribution or device-vendor advisories and the listed stable commits.

Exploitation context

The supplied CVSS vector describes local, low-complexity exploitation requiring low privileges and no user interaction, with potential confidentiality and availability impact. The CVE is not listed as KEV, and the supplied sources do not report active exploitation or public weaponization.

Researcher notes

The demonstrated failure is a slab out-of-bounds access caused by insufficient negative-offset validation. The patch direction and affected subsystem are clear. However, the bundle does not establish exploitability beyond the KASAN reproducer, identify active attacks, or provide reliable granular affected and fixed version boundaries.

Mitigation direction

  • Install a supported vendor kernel containing the applicable stable fix, then reboot into it.
  • Check distribution or appliance-vendor guidance for exact fixed package versions and supported mitigations.
  • Limit untrusted local access while patching remains outstanding.
  • Review the supplied Siemens advisories if affected Siemens products are deployed.

Validation and detection

  • Inventory running kernel versions across Linux hosts, appliances, containers hosts, and embedded systems.
  • Compare each kernel build against vendor advisories and the applicable stable fix commit.
  • Verify the patched kernel is active after reboot, not merely installed.
  • Identify systems using or exposing the cls_u32 traffic classifier.
  • Review kernel alerts for KASAN, u32_classify, cls_u32, or unexplained crashes without treating them as exploitation proof.
Prepared
Confidence
medium
Sources
11

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-2026-23204 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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
2ADP providers
10Source 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
7.1CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H1.85.2Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.1High
CVSS 3.1 vector shape for CVE-2026-23204Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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
other:ssvc
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxfbc2e7d9cf49e0bf89b9e91fd60a06851a855c5d, fbc2e7d9cf49e0bf89b9e91fd60a06851a855c5d, fbc2e7d9cf49e0bf89b9e91fd60a06851a855c5d, fbc2e7d9cf49e0bf89b9e91fd60a06851a855c5d, fbc2e7d9cf49e0bf89b9e91fd60a06851a855c5d, fbc2e7d9cf49e0bf89b9e91fd60a06851a855c5d, fbc2e7d9cf49e0bf89b9e91fd60a06851a855c5dunaffected
LinuxLinux2.6.35, 0, 5.10.260, 5.15.209, 6.1.167, 6.6.124, 6.12.70, 6.18.10, 6.19affected
Weakness

CWE details

No CWE listed

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