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CVE Record

CVE-2021-47355: atm: nicstar: Fix possible use-after-free in nicstar_cleanup()

In the Linux kernel, the following vulnerability has been resolved: atm: nicstar: Fix possible use-after-free in nicstar_cleanup() This module'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 analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel driver cleanup bug in the nicstar ATM network driver. A timer can keep running while the driver is being removed, leaving kernel code using freed memory. The public record does not provide CVSS, confirmed exploitation, or broad product impact beyond Linux kernel builds containing this driver.

Executive priority

Treat this as a targeted kernel maintenance item, not an emergency internet-wide incident. Prioritize patch confirmation on systems using specialized networking hardware or custom kernels, and include it in normal Linux kernel update cycles unless local driver exposure is confirmed.

Technical view

CVE-2021-47355 fixes a use-after-free in the Linux atm/nicstar cleanup path. The driver used del_timer(), which does not wait for an active timer handler to finish. The fix switches to del_timer_sync() so the handler is stopped before cleanup completes and cannot re-schedule itself.

Likely exposure

Exposure is most likely on Linux systems with the nicstar ATM driver present, built, loaded, or managed during hardware/module removal. The affected surface appears niche because it relates to an ATM network driver cleanup path, but kernel memory-safety bugs still deserve patch verification.

Exploitation context

The source bundle states KEV is false and provides no cited evidence of active exploitation, public weaponization, or a practical attack path. The described trigger is driver removal while a timer handler may still be active, so validation should focus on kernel version and driver presence, not internet exposure.

Researcher notes

The public record identifies the bug and fix pattern but omits CVSS, CWE, exploitability analysis, and distribution-specific package status. The key technical issue is asynchronous timer teardown during driver cleanup. Assess reachability through kernel configuration, module availability, and operational paths that remove the driver.

Mitigation direction

  • Update to a vendor kernel containing the referenced upstream stable fixes.
  • Prioritize systems where the nicstar ATM driver is built or loadable.
  • Check Linux distribution advisories for the exact fixed package version.
  • Disable or avoid loading unused nicstar ATM driver support where operationally safe.
  • Do not deploy directly from upstream commits without vendor compatibility review.

Validation and detection

  • Inventory running kernel versions against vendor advisories for CVE-2021-47355.
  • Check whether the nicstar ATM driver is present, built, or loaded.
  • Confirm the applied kernel contains the del_timer_sync cleanup fix.
  • Review asset classes using legacy ATM networking or specialized adapters.
  • Track patch status separately for each maintained kernel branch.
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-2021-47355 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

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2unaffected
LinuxLinux2.6.12, 0, 4.4.276, 4.9.276, 4.14.240, 4.19.198, 5.4.133, 5.10.51, 5.12.18, 5.13.3, 5.14affected
Weakness

CWE details

No CWE listed

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