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CVE Record

CVE-2021-46942: io_uring: fix shared sqpoll cancellation hangs

In the Linux kernel, the following vulnerability has been resolved: io_uring: fix shared sqpoll cancellation hangs [ 736.982891] INFO: task iou-sqp-4294:4295 blocked for more than 122 seconds. [ 736.982897] Call Trace: [ 736.982901] schedule+0x68/0xe0 [ 736.982903] io_uring_cancel_sqpoll+0xdb/0x110 [ 736.982908] io_sqpoll_cancel_cb+0x24/0x30 [ 736.982911] io_run_task_work_head+0x28/0x50 [ 736.982913] io_sq_thread+0x4e3/0x720 We call io_uring_cancel_sqpoll() one by one for each ctx either in sq_thread() itself or via task works, and it's intended to cancel all requests of a specified context. However the function uses per-task counters to track the number of inflight requests, so it counts more requests than available via currect io_uring ctx and goes to sleep for them to appear (e.g. from IRQ), that will never happen. Cancel a bit more than before, i.e. all ctxs that share sqpoll and continue to use shared counters. Don't forget that we should not remove ctx from the list before running that task_work sqpoll-cancel, otherwise the function wouldn't be able to find the context and will hang.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel availability bug in io_uring. In affected kernels, cancellation for shared SQPOLL contexts can wait forever, leaving a kernel worker task blocked. The sources do not show data theft, remote code execution, or confirmed exploitation.

Executive priority

Plan kernel remediation through normal patch governance, faster for multi-tenant or availability-sensitive Linux systems. There is no sourced active exploitation, but kernel hangs can still cause operational disruption.

Technical view

The fix changes sqpoll cancellation to cover all contexts sharing an SQPOLL thread. Previously, per-task inflight counters could include requests from other contexts, causing io_uring_cancel_sqpoll() to sleep waiting for requests that would never appear in the selected context.

Likely exposure

Exposure is most likely on Linux systems running affected 5.12-era or vendor-backported kernels where workloads use io_uring SQPOLL, especially shared SQPOLL contexts. Exact downstream package impact is not provided in the bundle.

Exploitation context

CISA KEV is false, and the bundle provides no cited exploitation reports. The public description shows a kernel cancellation hang, not a documented weaponized exploit path. Treat this as an availability risk unless vendor advisories or telemetry show more.

Researcher notes

The record lacks CVSS, CWE, and exact downstream package mapping. Source evidence centers on a hang in io_uring_cancel_sqpoll() caused by shared counters and context-list handling. Validate against exact kernel source or distributor changelog before declaring systems affected.

Mitigation direction

  • Update affected Linux kernels to vendor builds containing the referenced stable fixes.
  • Check distribution advisories for backported fixes matching CVE-2021-46942.
  • Prioritize hosts running io_uring-heavy services or multi-tenant workloads.
  • If patching is delayed, review vendor guidance for supported io_uring risk reduction.

Validation and detection

  • Inventory Linux kernel versions and map them to CVE-2021-46942 vendor advisories.
  • Confirm whether running workloads use io_uring with SQPOLL.
  • Review system logs for blocked io_uring SQPOLL worker tasks.
  • Verify patched hosts include the referenced stable commits or vendor equivalents.
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-2021-46942 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
3Source 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
LinuxLinux37d1e2e3642e2380750d7f35279180826f29660e, 37d1e2e3642e2380750d7f35279180826f29660eunaffected
LinuxLinux5.12, 0, 5.12.3, 5.13affected
Weakness

CWE details

No CWE listed

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