CVE-2021-47356

Kernel memory corruption via asynchronous timer deletion

Published May 21, 2024 · Updated May 11, 2026

Use-after-free in the mISDN HFC PCI driver in Linux allows local users to corrupt kernel memory during device removal. HFC_cleanup() calls del_timer(), which can return while its timer handler is still running and let that handler access driver state after removal frees it. Reaching the race requires the HFC PCI driver and device-removal path; successful exploitation can alter kernel memory or crash the system.

CVSS severity7.7
High
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the mISDN HFC PCI driver in Linux allows local users to corrupt kernel memory during device removal. HFC_cleanup() calls del_timer(), which can return while its timer handler is still running and let that handler access driver state after removal frees it. Reaching the race requires the HFC PCI driver and device-removal path; successful exploitation can alter kernel memory or crash the system.

The record

CVE
CVE-2021-47356
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 21, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.6.29
  2. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <009fc857c5f6fda81f2f7dd851b2d54193a8e733
  3. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <3ecd228c636ee17c14662729737fa07242a93cb0
  4. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <49331c07ef0f8fdfa42b30ba6a83a657b29d7fbe
  5. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <54ff3202928952a100c477248e65ac6db01258a7
  6. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <5f2818185da0fe82a932f0856633038b66faf124
  7. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <61370ff07e0acc657559a8fac02551dfeb9d3020
  8. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <7867ddc5f3de7f289aee63233afc0df4b62834c5
  9. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <b7ee9ae1e0cf55a037c4a99af2acc5d78cb7802d
  10. Affected versionversion=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <ed7c3739d0a07e2ec3ccbffe7e93cea01c438cda

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2.6.29; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <009fc857c5f6fda81f2f7dd851b2d54193a8e733; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <3ecd228c636ee17c14662729737fa07242a93cb0; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <49331c07ef0f8fdfa42b30ba6a83a657b29d7fbe; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <54ff3202928952a100c477248e65ac6db01258a7; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <5f2818185da0fe82a932f0856633038b66faf124; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <61370ff07e0acc657559a8fac02551dfeb9d3020; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <7867ddc5f3de7f289aee63233afc0df4b62834c5; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <b7ee9ae1e0cf55a037c4a99af2acc5d78cb7802d; version=87c5fa1bb42624254a2013cbbc3b170d6017f5d6 <ed7c3739d0a07e2ec3ccbffe7e93cea01c438cda
The Linux Kernel Organization · Linux Kernelversion=1da177e4c3f4 <009fc857c5f6; version=1da177e4c3f4 <3ecd228c636e; version=1da177e4c3f4 <49331c07ef0f; version=1da177e4c3f4 <54ff32029289; version=1da177e4c3f4 <5f2818185da0; version=1da177e4c3f4 <61370ff07e0a; version=1da177e4c3f4 <7867ddc5f3de; version=1da177e4c3f4 <b7ee9ae1e0cf; version=1da177e4c3f4 <ed7c3739d0a0

Published CVSS scores

7.7CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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