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CVE Record

CVE-2024-40920: net: bridge: mst: fix suspicious rcu usage in br_mst_set_state

In the Linux kernel, the following vulnerability has been resolved: net: bridge: mst: fix suspicious rcu usage in br_mst_set_state I converted br_mst_set_state to RCU to avoid a vlan use-after-free but forgot to change the vlan group dereference helper. Switch to vlan group RCU deref helper to fix the suspicious rcu usage warning.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2024-40920 is a Linux kernel networking fix in bridge VLAN/MST state handling. The public description says an RCU dereference helper was wrong after a change intended to avoid a VLAN use-after-free. The sources do not provide CVSS, confirmed impact, or active exploitation evidence.

Executive priority

Track and patch through normal Linux kernel maintenance unless your environment heavily uses bridge VLAN/MST networking. Escalate priority if vendor advisories assign higher severity or if affected kernels run on exposed multi-tenant infrastructure.

Technical view

The issue is in br_mst_set_state in Linux bridge MST code. A prior RCU conversion missed changing the VLAN group dereference helper, producing suspicious RCU usage. Kernel stable commits correct the helper usage. Public data does not define a reliable attack path, privilege requirement, or affected distribution matrix.

Likely exposure

Exposure is most relevant to Linux systems using kernel bridge VLAN or MST features. Exact exposure depends on kernel version, stable backports, and distribution packaging. The bundle lists Linux kernel identifiers and stable references, but does not provide a complete product-by-product affected list.

Exploitation context

The source bundle marks KEV as false and provides no cited evidence of active exploitation. The public description is a kernel correctness and safety fix, not a disclosed exploit report. Treat exploitation status as unconfirmed unless vendor advisories say otherwise.

Researcher notes

Evidence is thin: no CVSS, CWE, exploit narrative, or concrete impact is provided. The key technical clue is incorrect RCU VLAN group dereference in br_mst_set_state. Review referenced stable commits and downstream distro patches to determine whether local kernels contain the fix.

Mitigation direction

  • Check your distribution's kernel advisory for CVE-2024-40920 coverage.
  • Update to a kernel package containing the referenced stable fixes.
  • Prioritize systems using Linux bridge VLAN or MST functionality.
  • Avoid inventing compensating controls; follow vendor guidance if patching is delayed.

Validation and detection

  • Inventory running kernel versions across Linux hosts.
  • Identify systems using Linux bridge VLAN or MST features.
  • Compare installed kernel packages with distribution advisories and fixed builds.
  • Confirm kernel update deployment through package manager or asset data.
Prepared
Confidence
medium
Sources
7

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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ATT&CK lookup starting points

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CVE-2024-40920 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
3Timeline events
2ADP providers
6Source links

SSVC decision data

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

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

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux8ca9a750fc711911ef616ceb627d07357b04545e, 4488617e5e995a09abe4d81add5fb165674edb59, e43dd2b1ec746e105b7db5f9ad6ef14685a615a4, 3a7c1661ae1383364cd6092d851f5e5da64d476b, a2b01e65d9ba8af2bb086d3b7288ca53a07249ac, 6.8.12unaffected
LinuxLinux6.1.93, 6.6.33, 6.9.3unaffected
Weakness

CWE details

No CWE listed

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