dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-42373

MEDIUM · 5.5 CVSS v3.1 Published 2021-11-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
57/100
Remediation priority · Elevated
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A NULL pointer dereference in Busybox's man applet leads to denial of service when a section name is supplied but no page argument is given

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A NULL pointer dereference vulnerability exists in Busybox's man applet. When a section name (such as '1' or '2') is supplied as an argument without a corresponding manual page, the application attempts to dereference a NULL pointer, causing a crash and denial of service.

MitigationUpgrade Busybox to a patched version that includes proper NULL pointer validation in the man applet, or implement input validation to ensure a page argument is provided before processing.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FedoraOperating system
Affected:= 33= 34
BusyboxApplication
Affected:= 1.33.0= 1.33.1
Cloud BackupApplication
Affected:all versions
Hci Management NodeApplication
Affected:all versions
SolidfireApplication
Affected:all versions
H300s FirmwareOperating system
Affected:all versions
H500s FirmwareOperating system
Affected:all versions
H700s FirmwareOperating system
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Busybox version
    Run 'busybox --version' or check the busybox binary with 'busybox 2>&1 | head -1' to retrieve the version string
    Affected if The version is 1.33.0 or 1.33.1, which are the known vulnerable versions listed in the CVE
  2. Verify man applet is available
    Run 'busybox --list | grep man' or try executing 'busybox man --help' to confirm the man applet is compiled into the Busybox binary
    Affected if The man applet is present in the Busybox build, making it a potential attack vector
  3. Confirm man binary/symlink points to Busybox
    Run 'which man' or 'ls -la /bin/man /usr/bin/man 2>/dev/null' to check if the man command is provided by Busybox
    Affected if The man command resolves to Busybox (e.g., /bin/busybox or /bin/sh -> busybox), indicating the vulnerable applet is in use
  4. Test for crash condition
    Execute 'man 1' or 'man 2' (a numeric section argument without a valid man page name) using the Busybox man applet to trigger the NULL pointer dereference
    Affected if The command causes a crash, segmentation fault, or abnormal termination, confirming the vulnerability is present and exploitable

You are affected if Busybox version 1.33.0 or 1.33.1 is installed with the man applet enabled, and executing 'man <number>' triggers a crash due to the NULL pointer dereference.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Busybox to a patched version that includes proper NULL pointer validation in the man applet, or implement input validation to ensure a page argument is provided before processing.

Recommended fix Moderate confidence

Busybox 1.34.0 or later

  1. Identify the Busybox binary or package in use on the system
  2. Check the current installed version using: `busybox --version` or `rpm -q busybox` / `dpkg -l busybox`
  3. Upgrade Busybox to version 1.34.0 or later which contains the fix for the NULL pointer dereference in the man applet
  4. On Fedora systems: `sudo dnf update busybox`
  5. On other Linux systems: download and install the updated package from your distribution's package repository
  6. Verify the upgrade was successful by running `busybox --version` again
  7. Test the man applet functionality to confirm it no longer crashes when invoked with a section name but no page argument
Caveat Minimal risk - Busybox upgrades are generally backward compatible for standard functionality

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-42373 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data