CVE-2021-42376

Shell crash via mishandled control-byte encoding

Published Nov 15, 2021 · Updated Aug 4, 2024

NULL pointer dereference in BusyBox hush before 1.34.0 allows local users to crash the shell by supplying a crafted command. In shell/hush.c, encode_string and parse_stream fail to encode a 0x03 control byte as a special-variable reference before subsequent parsing dereferences a null pointer. Triggering requires the rare condition that filtered command input preserves the control byte; the result is a hush process crash, with no reported data disclosure or modification.

CVSS severity5.5
Medium
EPSS probability0.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

NULL pointer dereference in BusyBox hush before 1.34.0 allows local users to crash the shell by supplying a crafted command. In shell/hush.c, encode_string and parse_stream fail to encode a 0x03 control byte as a special-variable reference before subsequent parsing dereferences a null pointer. Triggering requires the rare condition that filtered command input preserves the control byte; the result is a hush process crash, with no reported data disclosure or modification.

The record

CVE
CVE-2021-42376
Published
Nov 15, 2021
Updated
Aug 4, 2024
Vendor
BusyBox
Product
BusyBox
Classifications
CWE-476
Attack vector
local
Privileges
authenticated

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

Compare your product and version with the public record. A matching version still requires validation against your environment.

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

5.5NIST NVDCVSS: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-476NULL Pointer Dereference

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo