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CVE Record

CVE-2021-47321: watchdog: Fix possible use-after-free by calling del_timer_sync()

In the Linux kernel, the following vulnerability has been resolved: watchdog: Fix possible use-after-free by calling del_timer_sync() This driver's remove path calls del_timer(). However, that function does not wait until the timer handler finishes. This means that the timer handler may still be running after the driver's remove function has finished, which would result in a use-after-free. Fix by calling del_timer_sync(), which makes sure the timer handler has finished, and unable to re-schedule itself.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

A Linux kernel watchdog driver had a timing bug during driver removal. The driver could finish removal while its timer callback was still running, creating a possible use-after-free in kernel memory. Public sources show kernel stable fixes, but do not provide CVSS, distribution impact, or confirmed exploitation.

Executive priority

Treat as a patch-tracking item rather than an emergency based on available evidence. The bug is in kernel code, so unresolved exposure matters, but no source shows active exploitation or a scored severity.

Technical view

The remove path used del_timer(), which does not wait for an active timer handler to finish. The fix replaces that behavior with del_timer_sync(), preventing the handler from running after teardown or rescheduling itself. The CVE record lists affected Linux kernel versions and multiple stable commit references.

Likely exposure

Exposure is most likely on systems running affected Linux kernel versions with the relevant watchdog driver present and removable. Distribution-specific package status is not provided in the source bundle, so fleet exposure needs kernel and vendor advisory validation.

Exploitation context

The source bundle does not report active exploitation, public exploit code, or KEV listing. Trigger context appears tied to driver removal while a timer handler may still execute, but sources do not describe practical attack requirements or privilege needed.

Researcher notes

Key uncertainty is exploitability. The public text describes a kernel use-after-free race in driver teardown, but not an attacker-controlled path. Review the stable commits and downstream patches to identify the exact driver, affected configurations, and whether local privilege boundaries are relevant.

Mitigation direction

  • Update to a Linux kernel or vendor package containing the stable fixes.
  • Check Linux distribution advisories for backported fixes matching your deployed kernels.
  • Prioritize internet-facing or multi-tenant systems if the affected driver is present.
  • Avoid unnecessary removal or unloading of the affected watchdog driver until patched.

Validation and detection

  • Inventory deployed Linux kernel versions across servers, appliances, and embedded systems.
  • Check whether the relevant watchdog driver is built, loaded, or used.
  • Map installed kernels to vendor advisories or the referenced stable commits.
  • Confirm patched kernels are running after maintenance windows and reboots.
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

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-2021-47321 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
LinuxLinux7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dc, 7c25f8c9f67708e6464d2221bc311cbd99e950dcunaffected
LinuxLinux4.3, 0, 4.4.276, 4.9.276, 4.14.240, 4.19.198, 5.4.134, 5.10.52, 5.12.19, 5.13.4, 5.14affected
Weakness

CWE details

No CWE listed

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