CVE-2021-35477

Kernel-memory disclosure via reordered BPF verifier stores

Published Aug 2, 2021 · Updated Aug 4, 2024

Information disclosure in the Linux kernel through 5.13.7 allows local users to read arbitrary kernel memory via an unprivileged BPF program. The BPF verifier inserts a preempting zero store but incorrectly assumes it completes before a dependent load, enabling speculative use of an attacker-controlled scalar. Exploitation requires permission to load an unprivileged BPF program and exposes memory through a cache side channel without modifying kernel state.

CVSS severity5.5
Medium
EPSS probability0.46%
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 the Linux kernel through 5.13.7 allows local users to read arbitrary kernel memory via an unprivileged BPF program. The BPF verifier inserts a preempting zero store but incorrectly assumes it completes before a dependent load, enabling speculative use of an attacker-controlled scalar. Exploitation requires permission to load an unprivileged BPF program and exposes memory through a cache side channel without modifying kernel state.

The record

CVE
CVE-2021-35477
Published
Aug 2, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-203, T1005
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

2.1NVDAV:L/AC:L/Au:N/C:P/I:N/A:N
5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
4.4Amazon LinuxCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N
6.5SUSECVSS:3.1/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-203Observable Discrepancy
T1005Data from Local System

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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