CVE-2021-42375

Shell crash via trailing VSLENGTH garbage

Published Nov 15, 2021 · Updated Apr 23, 2025

Denial of service in the BusyBox ash applet before 1.34.0 allows local users to crash the shell via a crafted command line. The VSLENGTH parser accepts trailing garbage after a variable-length expression and then mistakes following characters for reserved syntax. Reachability requires control of ash command-line arguments under rare filtered-input conditions, and the documented consequence is termination of that shell process.

CVSS severity5.5
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the BusyBox ash applet before 1.34.0 allows local users to crash the shell via a crafted command line. The VSLENGTH parser accepts trailing garbage after a variable-length expression and then mistakes following characters for reserved syntax. Reachability requires control of ash command-line arguments under rare filtered-input conditions, and the documented consequence is termination of that shell process.

The record

CVE
CVE-2021-42375
Published
Nov 15, 2021
Updated
Apr 23, 2025
Vendor
BusyBox
Product
BusyBox
Classifications
CWE-159, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Apr 23, 2025Record 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=unspecified <1.34.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

BusyBox · BusyBoxversion=unspecified <1.34.0

Published CVSS scores

5.5CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
1.9National Vulnerability DatabaseAV:L/AC:M/Au:N/C:N/I:N/A:P
4.1SUSECVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
5.5National Vulnerability DatabaseCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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-159Improper Handling of Invalid Use of Special Elements
T1499.004Application or System Exploitation

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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