CVE-2021-47040

Kernel code execution via provided-buffer size overflow

Published Feb 28, 2024 · Updated Aug 5, 2026

Buffer overflow in the Linux kernel starting with 5.8 allows local users to execute code in the kernel via crafted io_uring buffers. In io_provide_buffers_prep(), unchecked multiplication of attacker-controlled buffer length and count can wrap, causing access_ok to validate less memory than later buffer-selection I/O trusts. An unprivileged local account can trigger kernel memory disclosure, corruption, or a crash without user interaction.

CVSS severity7.8
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in the Linux kernel starting with 5.8 allows local users to execute code in the kernel via crafted io_uring buffers. In io_provide_buffers_prep(), unchecked multiplication of attacker-controlled buffer length and count can wrap, causing access_ok to validate less memory than later buffer-selection I/O trusts. An unprivileged local account can trigger kernel memory disclosure, corruption, or a crash without user interaction.

The record

CVE
CVE-2021-47040
Published
Feb 28, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-120, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=5.8
  2. Affected versionversion=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <38134ada0ceea3e848fe993263c0ff6207fd46e7
  3. Affected versionversion=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <51bf90901952aaac564bbdb36b2b503050c53dd9
  4. Affected versionversion=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <84b8c266c4bfe9ed5128e13253c388deb74b1b03
  5. Affected versionversion=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <cbbc13b115b8f18e0a714d89f87fbdc499acfe2d

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.8; version=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <38134ada0ceea3e848fe993263c0ff6207fd46e7; version=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <51bf90901952aaac564bbdb36b2b503050c53dd9; version=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <84b8c266c4bfe9ed5128e13253c388deb74b1b03; version=efe68c1ca8f49e8c06afd74b699411bfbb8ba1ff <cbbc13b115b8f18e0a714d89f87fbdc499acfe2d

Published CVSS scores

7.8Linux Kernel CVE teamCVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
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

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Your stack

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