CVE-2021-47355

Local kernel memory corruption via timer race

Published May 21, 2024 · Updated May 11, 2026

Use-after-free in the Linux kernel NICStar ATM driver allows local users to corrupt kernel memory during device removal. nicstar_cleanup calls del_timer without waiting for the timer handler, allowing the callback to access driver state after the remove path frees it. The NICStar driver must be active, and device removal must race its timer callback; successful exploitation grants kernel-level read and write access or crashes the system.

CVSS severity7.8
High
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in the Linux kernel NICStar ATM driver allows local users to corrupt kernel memory during device removal. nicstar_cleanup calls del_timer without waiting for the timer handler, allowing the callback to access driver state after the remove path frees it. The NICStar driver must be active, and device removal must race its timer callback; successful exploitation grants kernel-level read and write access or crashes the system.

The record

CVE
CVE-2021-47355
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1068
Attack vector
local
Privileges
authenticated

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=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <2f958b6f6ba0854b39be748d21dfe71e0fe6580f
  2. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <34e7434ba4e97f4b85c1423a59b2922ba7dff2ea
  3. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <4e2a0848ea2cab0716d46f85a8ccd5fa9a493e51
  4. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <5b991df8881088448cb223e769e37cab8dd40706
  5. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <99779c9d9ffc7775da6f7fd8a7c93ac61657bed5
  6. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <a7a7b2848312cc4c3a42b6e42a8ab2e441857aba
  7. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <a7f7c42e31157d1f0871d6a8e1a0b73a6b4ea785
  8. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bdf5334250c69fabf555b7322c75249ea7d5f148
  9. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <c471569632654e57c83512e0fc1ba0dbb4544ad6
  10. Affected versionversion=2.6.12

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <2f958b6f6ba0854b39be748d21dfe71e0fe6580f; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <34e7434ba4e97f4b85c1423a59b2922ba7dff2ea; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <4e2a0848ea2cab0716d46f85a8ccd5fa9a493e51; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <5b991df8881088448cb223e769e37cab8dd40706; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <99779c9d9ffc7775da6f7fd8a7c93ac61657bed5; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <a7a7b2848312cc4c3a42b6e42a8ab2e441857aba; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <a7f7c42e31157d1f0871d6a8e1a0b73a6b4ea785; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bdf5334250c69fabf555b7322c75249ea7d5f148; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <c471569632654e57c83512e0fc1ba0dbb4544ad6; version=2.6.12

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1068Exploitation for Privilege Escalation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo