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CVE Record

CVE-2025-40164: usbnet: Fix using smp_processor_id() in preemptible code warnings

In the Linux kernel, the following vulnerability has been resolved: usbnet: Fix using smp_processor_id() in preemptible code warnings Syzbot reported the following warning: BUG: using smp_processor_id() in preemptible [00000000] code: dhcpcd/2879 caller is usbnet_skb_return+0x74/0x490 drivers/net/usb/usbnet.c:331 CPU: 1 UID: 0 PID: 2879 Comm: dhcpcd Not tainted 6.15.0-rc4-syzkaller-00098-g615dca38c2ea #0 PREEMPT(voluntary) Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120 check_preemption_disabled+0xd0/0xe0 lib/smp_processor_id.c:49 usbnet_skb_return+0x74/0x490 drivers/net/usb/usbnet.c:331 usbnet_resume_rx+0x4b/0x170 drivers/net/usb/usbnet.c:708 usbnet_change_mtu+0x1be/0x220 drivers/net/usb/usbnet.c:417 __dev_set_mtu net/core/dev.c:9443 [inline] netif_set_mtu_ext+0x369/0x5c0 net/core/dev.c:9496 netif_set_mtu+0xb0/0x160 net/core/dev.c:9520 dev_set_mtu+0xae/0x170 net/core/dev_api.c:247 dev_ifsioc+0xa31/0x18d0 net/core/dev_ioctl.c:572 dev_ioctl+0x223/0x10e0 net/core/dev_ioctl.c:821 sock_do_ioctl+0x19d/0x280 net/socket.c:1204 sock_ioctl+0x42f/0x6a0 net/socket.c:1311 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl fs/ioctl.c:892 [inline] __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f For historical and portability reasons, the netif_rx() is usually run in the softirq or interrupt context, this commit therefore add local_bh_disable/enable() protection in the usbnet_resume_rx().

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-40164 is a Linux kernel usbnet flaw reported by syzbot. It can trigger a kernel warning when USB networking code runs in a context where CPU-specific access is unsafe. The sources do not show data theft, remote code execution, or active exploitation.

Executive priority

Handle through normal kernel patch management unless USB networking is material to production, appliances, or embedded fleets. There is no sourced evidence of active exploitation, but kernel correctness issues should not be left untracked in managed Linux baselines.

Technical view

The issue is in drivers/net/usb/usbnet.c. During MTU change and receive resume paths, usbnet_resume_rx() can reach usbnet_skb_return(), where smp_processor_id() is used from preemptible code. The kernel fix adds local_bh_disable()/local_bh_enable() protection around usbnet_resume_rx() behavior.

Likely exposure

Exposure is limited to Linux systems running affected kernel versions with the usbnet driver path in use, typically USB network adapters or devices using USB networking. The source bundle lists Linux as affected and provides stable kernel commit references, but does not map specific distribution packages.

Exploitation context

The evidence is a syzbot-triggered kernel warning involving dhcpcd and MTU handling. The bundle marks KEV as false, and no cited source states active exploitation, public exploit code, or real-world abuse.

Researcher notes

This appears to be a kernel concurrency/context correctness fix rather than a clearly demonstrated security exploit. Impact is not quantified by CVSS or CWE in the provided record. Researchers should focus on affected kernel lineage, usbnet usage, and whether vendor backports include the local_bh protection.

Mitigation direction

  • Update to a Linux kernel build containing the referenced stable fixes.
  • Check distribution vendor advisories for the corrected package version.
  • Prioritize systems using USB network adapters or embedded USB networking.
  • Follow vendor guidance if running custom or long-term kernel builds.

Validation and detection

  • Inventory Linux kernel versions across affected hosts and images.
  • Identify systems loading or depending on usbnet-based drivers.
  • Confirm vendor kernel changelogs include CVE-2025-40164 or the referenced commits.
  • Review kernel logs for related preemptible-code warnings if USB networking is used.
Prepared
Confidence
medium
Sources
9

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.

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CVE-2025-40164 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
1ADP providers
8Source 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

CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux43daa96b166c3cf5ff30dfac0c5efa2620e4beab, 43daa96b166c3cf5ff30dfac0c5efa2620e4beab, 43daa96b166c3cf5ff30dfac0c5efa2620e4beab, 43daa96b166c3cf5ff30dfac0c5efa2620e4beab, 43daa96b166c3cf5ff30dfac0c5efa2620e4beab, 43daa96b166c3cf5ff30dfac0c5efa2620e4beab, 43daa96b166c3cf5ff30dfac0c5efa2620e4beabunaffected
LinuxLinux4.7, 0, 5.10.259, 5.15.199, 6.1.162, 6.6.122, 6.12.64, 6.17.5, 6.18affected
Weakness

CWE details

No CWE listed

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