CVE-2021-20239

Kernel-address disclosure via BPF pointer-probing oracle

Published May 28, 2021 · Updated Aug 3, 2024

Information disclosure in sockopt BPF hooks in Linux Kernel before 5.4.92 allows local users to probe valid kernel addresses. BPF cgroup programs return a different error when a user-supplied pointer names a valid kernel address, creating an address-validity oracle. A user with CAP_NET_ADMIN must first attach a filter; after any filter is in use, an unprivileged local user can map kernel memory layout.

CVSS severity3.3
Low
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

Information disclosure in sockopt BPF hooks in Linux Kernel before 5.4.92 allows local users to probe valid kernel addresses. BPF cgroup programs return a different error when a user-supplied pointer names a valid kernel address, creating an address-validity oracle. A user with CAP_NET_ADMIN must first attach a filter; after any filter is in use, an unprivileged local user can map kernel memory layout.

The record

CVE
CVE-2021-20239
Published
May 28, 2021
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-822, CWE-119
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=kernel 5.4.92

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=kernel 5.4.92

Published CVSS scores

3.3NIST National Vulnerability DatabaseCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
6.5Trend Micro Zero Day InitiativeCVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/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.

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-822Untrusted Pointer Dereference
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer

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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