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CVE Record

CVE-2021-47123: io_uring: fix ltout double free on completion race

In the Linux kernel, the following vulnerability has been resolved: io_uring: fix ltout double free on completion race Always remove linked timeout on io_link_timeout_fn() from the master request link list, otherwise we may get use-after-free when first io_link_timeout_fn() puts linked timeout in the fail path, and then will be found and put on master's free.

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 memory-management flaw in io_uring. A race during linked timeout completion could cause double free or use-after-free behavior. The public bundle does not provide CVSS, impact, or exploitation evidence, so urgency depends on whether affected kernel versions are present and reachable by untrusted local workloads.

Executive priority

Treat as a kernel patch-management item with uncertain severity. Prioritize validation on shared Linux infrastructure and environments running untrusted code, but avoid emergency assumptions unless vendor guidance or new exploitation evidence changes the risk picture.

Technical view

The resolved defect is in io_uring linked timeout handling. The fix always removes the linked timeout from the master request link list in io_link_timeout_fn(), preventing a completion race where the timeout is freed in one path and later found and freed again from the master request.

Likely exposure

Exposure is limited to Linux systems running affected kernel versions identified in the CVE record. The bundle lists Linux kernel 5.11, 5.12.10, and 5.13 data, but does not provide complete distro package mappings or remote exposure details.

Exploitation context

The bundle does not report active exploitation, and KEV is false. It provides kernel fix references but no exploit status, proof-of-concept, attack requirements, or confirmed impact beyond double free and use-after-free risk.

Researcher notes

Evidence is narrow: the record describes a resolved io_uring linked-timeout race causing double free or use-after-free. No CVSS, CWE, exploit maturity, privilege requirement, or distro-specific fixed version is included in the provided bundle.

Mitigation direction

  • Update affected Linux kernels to versions containing the referenced stable fixes.
  • Check Linux distribution advisories for exact fixed package versions.
  • Prioritize shared systems where untrusted local users or workloads can access io_uring.
  • Use vendor-supported hardening or io_uring restrictions only if patching is delayed.

Validation and detection

  • Inventory Linux kernel versions across servers, containers, and base images.
  • Map installed distro kernel packages to vendor advisories for CVE-2021-47123.
  • Confirm whether deployed kernels include the referenced stable commits.
  • Review multi-user and workload-hosting systems before lower-risk single-purpose hosts.
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

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-2021-47123 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
LinuxLinux90cd7e424969d29aff653333b4dcb4e2e199d791, 90cd7e424969d29aff653333b4dcb4e2e199d791unaffected
LinuxLinux5.11, 0, 5.12.10, 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.