dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-42377

CRITICAL · 9.8 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 →
100/100
Remediation priority · Urgent
Remotely reachable No privileges 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
An attacker-controlled pointer free in Busybox's hush applet leads to denial of service and possible code execution when processing a crafted shell command, due to the shell mishandling the &&& string. This may be used for remote code execution under rare conditions of filtered command input.

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

CVE-2021-42377 is a use-after-free vulnerability in BusyBox's hush shell applet where an attacker-controlled pointer is freed, leading to denial of service and potential code execution. The vulnerability is triggered when the shell mishandles a specially crafted '&&&' string in shell commands, allowing memory corruption under specific conditions of filtered command input.

MitigationUpdate BusyBox to a version containing the security patch for CVE-2021-42377, or rebuild BusyBox with the fixed hush applet. Test shell functionality after the update to ensure the fix does not break existing shell scripts.

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 BusyBox version
    Run 'busybox --version' or 'busybox | head -1' to get the installed BusyBox version
    Affected if Version is 1.33.0 or 1.33.1 (the specific affected versions listed)
  2. Verify hush shell is in use
    Run 'ls -la /bin/sh' to check which shell /bin/sh points to, or run 'busybox --help' and look for hush in the list of applets
    Affected if The system uses hush as the default shell (indicated by /bin/sh pointing to hush or busybox hush being available)
  3. Check if hush applet is enabled in BusyBox
    Run 'busybox --list' or check if 'busybox hush --help' works to confirm the hush applet is compiled into the binary
    Affected if The hush applet is present and enabled in the BusyBox binary
  4. Test vulnerability with crafted input
    Run a test command using the vulnerable pattern: try executing 'echo test &&& echo test' through the hush shell - observe for crashes, hangs, or use-after-free errors
    Affected if The command triggers a crash, memory error, or unexpected behavior indicating the use-after-free is present

A system is affected if it runs BusyBox version 1.33.0 or 1.33.1 with the hush shell applet enabled and the '&&&' pattern triggers a crash or memory error.

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

Update BusyBox to a version containing the security patch for CVE-2021-42377, or rebuild BusyBox with the fixed hush applet. Test shell functionality after the update to ensure the fix does not break existing shell scripts.

Recommended fix High confidence

BusyBox 1.33.2 or later (1.34.x stable recommended); Fedora 33/34 users should update via `dnf update` to receive the patched busybox package

  1. Identify the BusyBox version currently installed: run `busybox --version` or check your system's package manager
  2. For standalone BusyBox: Download and install BusyBox 1.33.2 or later (1.34.x recommended) from the official BusyBox website or distribution repositories
  3. For Fedora systems: Run `sudo dnf update busybox` to fetch the patched version released by Fedora
  4. For NetApp products (Cloud Backup, HCI Management Node, Solidfire, H300s/H500s/H700s): Consult NetApp's advisory at security.netapp.com for vendor-specific patches or firmware updates
  5. Verify the fix by confirming the new version is installed: `busybox --version`
  6. Test critical shell scripts to ensure compatibility with the updated BusyBox version
Caveat BusyBox updates are generally backward-compatible; however, test any custom shell scripts using hush features as minor behavioral changes in edge cases are possible

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 / QA1.0 h
8.0 hours of engineering $1,390
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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-2021-42377 in production — separate from our analysis above.

No notes yet

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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