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CVE Record

CVE-2021-46959: spi: Fix use-after-free with devm_spi_alloc_*

In the Linux kernel, the following vulnerability has been resolved: spi: Fix use-after-free with devm_spi_alloc_* We can't rely on the contents of the devres list during spi_unregister_controller(), as the list is already torn down at the time we perform devres_find() for devm_spi_release_controller. This causes devices registered with devm_spi_alloc_{master,slave}() to be mistakenly identified as legacy, non-devm managed devices and have their reference counters decremented below 0. ------------[ cut here ]------------ WARNING: CPU: 1 PID: 660 at lib/refcount.c:28 refcount_warn_saturate+0x108/0x174 [<b0396f04>] (refcount_warn_saturate) from [<b03c56a4>] (kobject_put+0x90/0x98) [<b03c5614>] (kobject_put) from [<b0447b4c>] (put_device+0x20/0x24) r4:b6700140 [<b0447b2c>] (put_device) from [<b07515e8>] (devm_spi_release_controller+0x3c/0x40) [<b07515ac>] (devm_spi_release_controller) from [<b045343c>] (release_nodes+0x84/0xc4) r5:b6700180 r4:b6700100 [<b04533b8>] (release_nodes) from [<b0454160>] (devres_release_all+0x5c/0x60) r8:b1638c54 r7:b117ad94 r6:b1638c10 r5:b117ad94 r4:b163dc10 [<b0454104>] (devres_release_all) from [<b044e41c>] (__device_release_driver+0x144/0x1ec) r5:b117ad94 r4:b163dc10 [<b044e2d8>] (__device_release_driver) from [<b044f70c>] (device_driver_detach+0x84/0xa0) r9:00000000 r8:00000000 r7:b117ad94 r6:b163dc54 r5:b1638c10 r4:b163dc10 [<b044f688>] (device_driver_detach) from [<b044d274>] (unbind_store+0xe4/0xf8) Instead, determine the devm allocation state as a flag on the controller which is guaranteed to be stable during cleanup.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel bug in SPI device cleanup. Under specific driver removal or unbind paths, the kernel can mishandle reference counts and trigger a use-after-free condition. The sources do not provide CVSS, impact scoring, or active exploitation evidence.

Executive priority

Treat this as a patch-management item for Linux and embedded fleets, not an emergency based on current evidence. Prioritize systems with SPI hardware, custom kernels, or appliance firmware where kernel updates lag.

Technical view

During spi_unregister_controller(), devres state was queried after the devres list had already been torn down. devm_spi_alloc_{master,slave}() controllers could be misclassified as legacy controllers, causing extra put_device/kobject_put handling and refcount underflow. The fix stores devm allocation state in a stable controller flag.

Likely exposure

Exposure appears limited to Linux systems using affected kernel versions and SPI controller drivers that allocate controllers through devm_spi_alloc_master or devm_spi_alloc_slave, especially during driver detach, device unbind, or cleanup paths.

Exploitation context

The bundle marks KEV as false and gives no public evidence of exploitation. The provided trace shows a kernel warning during driver unbind, but the sources do not prove a practical attacker path or privilege requirement.

Researcher notes

The affected metadata is incomplete and includes version strings plus upstream stable commit references. No CWE, CVSS vector, or exploitability details are supplied. Analysis should focus on kernel version lineage, SPI controller usage, and whether the stable controller flag fix is present.

Mitigation direction

  • Update affected Linux kernels to vendor-supported builds containing the referenced stable fixes.
  • Check distribution or device vendor advisories for the exact fixed package version.
  • Prioritize embedded, appliance, and custom-kernel systems using SPI hardware or SPI controller drivers.
  • Avoid ad hoc driver changes unless validated against upstream stable patches.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and embedded devices.
  • Identify systems with SPI controller drivers or custom kernel modules using SPI controller allocation.
  • Map running kernels to vendor fixed releases or the referenced stable commits.
  • Review kernel logs for refcount warnings during SPI driver detach or device unbind.
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

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CVE-2021-46959 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
10Source 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
LinuxLinuxa4add022c1552b0d51a0b89a4781919d6ebac4f9, 0870525cf94bc27907e94ce99afb6d7239ffd2f5, 8c45a1c6c951bbe7f95db78fcab46f7337364468, 234b432c7b6184b2d6c5ba2c55f0dd5023c0edf0, 3e04a4976addbedcad326f47b0dd4efc570a1fac, 5e844cc37a5cbaa460e68f9a989d321d63088a89, 5e844cc37a5cbaa460e68f9a989d321d63088a89, 5e844cc37a5cbaa460e68f9a989d321d63088a89, 5e844cc37a5cbaa460e68f9a989d321d63088a89, bd1a5b2307279029faaddbecf2f2ac25eaef8dc6unaffected
LinuxLinux5.10, 0, 4.4.271, 4.9.271, 4.14.233, 4.19.191, 5.4.119, 5.10.37, 5.11.21, 5.12.4, 5.13affected
Weakness

CWE details

No CWE listed

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