CVE-2021-42377Network attack vector

Shell crash or code execution via invalid free

Published Nov 15, 2021 · Updated Aug 4, 2024

Invalid pointer release in BusyBox hush 1.33.0 through 1.33.1 allows attackers to crash the shell or execute code via a crafted command. The hush parser mishandles the &&& token and frees an attacker-controlled pointer while processing the command line. Reachability requires an application or service to pass attacker-controlled text containing an ampersand to the optional hush applet; the usual result is a subprocess crash, while code execution requires rare filtered-input conditions.

CVSS severity9.8
Critical
EPSS probability3.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Invalid pointer release in BusyBox hush 1.33.0 through 1.33.1 allows attackers to crash the shell or execute code via a crafted command. The hush parser mishandles the &&& token and frees an attacker-controlled pointer while processing the command line. Reachability requires an application or service to pass attacker-controlled text containing an ampersand to the optional hush applet; the usual result is a subprocess crash, while code execution requires rare filtered-input conditions.

The record

CVE
CVE-2021-42377
Published
Nov 15, 2021
Updated
Aug 4, 2024
Vendor
BusyBox
Product
BusyBox
Classifications
CWE-763, CWE-590, T1059.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 15, 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?

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 vectornetwork
Required privilegesunauthenticated

What is affected?

BusyBox · BusyBoxversion=unspecified <1.34.0

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-763Release of Invalid Pointer or Reference
CWE-590Free of Memory not on the Heap
T1059.004Command and Scripting Interpreter: Unix Shell

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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