CVE-2021-47375

Kernel crash via blktrace use-after-free race

Published May 21, 2024 · Updated May 11, 2026

Use-after-free in Linux blktrace allows local users to crash the kernel by racing trace removal with block I/O activity. The sysfs removal path frees a relay buffer while trace_note_tsk can still reach its blk_trace entry through running_trace_list and dereference the freed buffer. Reaching the race requires access to two block devices, BLKTRACE ioctls, sysfs trace controls, and precise concurrent timing.

CVSS severity6.2
Medium
EPSS probability0.25%
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 Linux blktrace allows local users to crash the kernel by racing trace removal with block I/O activity. The sysfs removal path frees a relay buffer while trace_note_tsk can still reach its blk_trace entry through running_trace_list and dereference the freed buffer. Reaching the race requires access to two block devices, BLKTRACE ioctls, sysfs trace controls, and precise concurrent timing.

The record

CVE
CVE-2021-47375
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1499
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=2.6.30
  2. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <3815fe7371d2411ce164281cef40d9fc7b323dee
  3. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <488da313edf3abea7f7733efe011c96b23740ab5
  4. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <5afedf670caf30a2b5a52da96eb7eac7dee6a9c9
  5. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <677e362ba807f3aafe6f405c07e0b37244da5222
  6. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <a5f8e86192612d0183047448d8bbe7918b3f1a26
  7. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <d56171d9360c0170c5c5f8f7e2362a2e999eca40
  8. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <dacfd5e4d1142bfb3809aab3634a375f6f373269
  9. Affected versionversion=c71a896154119f4ca9e89d6078f5f63ad60ef199 <ebb8d26d93c3ec3c7576c52a8373a2309423c069

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2.6.30; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <3815fe7371d2411ce164281cef40d9fc7b323dee; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <488da313edf3abea7f7733efe011c96b23740ab5; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <5afedf670caf30a2b5a52da96eb7eac7dee6a9c9; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <677e362ba807f3aafe6f405c07e0b37244da5222; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <a5f8e86192612d0183047448d8bbe7918b3f1a26; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <d56171d9360c0170c5c5f8f7e2362a2e999eca40; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <dacfd5e4d1142bfb3809aab3634a375f6f373269; version=c71a896154119f4ca9e89d6078f5f63ad60ef199 <ebb8d26d93c3ec3c7576c52a8373a2309423c069

Published CVSS scores

6.2CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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
T1499Endpoint Denial of Service

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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