dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-33643

CRITICAL · 9.1 CVSS v3.1 Published 2022-08-10
Fix available
A fix is available. Upgrade to 1.2.21 or later.
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 who submits a crafted tar file with size in header struct being 0 may be able to trigger an calling of malloc(0) for a variable gnu_longlink, causing an out-of-bounds read.

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 crafted tar file with size field set to 0 in the header struct triggers malloc(0) for the gnu_longlink variable, leading to an out-of-bounds read vulnerability during tar archive processing.

MitigationUpdate the tar processing library/code to validate the size field in tar headers before allocating memory, rejecting or properly handling archives with zero-size headers to prevent the malloc(0) call.

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:= 35= 36= 37
LibtarApplication
Affected:< 1.2.21
OpeneulerOperating system
Affected:= 20.03= 22.03

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
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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 if libtar library is installed
    On Linux systems, run: find /usr -name 'libtar*' 2>/dev/null or check your package manager (dnf/rpm for Fedora, yum/rpm for OpenEuler) for installed libtar packages
    Affected if libtar is installed with version less than 1.2.21 (run: rpm -qa | grep libtar or dpkg -l | grep libtar)
  2. Check libtar version directly
    If libtar.so or libtar.a is found, run: rpm -q --changelog libtar 2>/dev/null or check the library version with: strings libtar.so | grep -i version | head -5
    Affected if Version cannot be determined or shows a version prior to 1.2.21
  3. Identify applications using libtar
    Search for binaries that link to libtar: ldd /path/to/binary 2>/dev/null | grep libtar or scan application binaries with: strings binary_file | grep libtar
    Affected if Any application that processes tar files links to a vulnerable version of libtar
  4. Check system tar utilities on Fedora
    On Fedora systems, verify the tar utility version: rpm -q tar and examine if custom Fedora patches exist in: rpm -q --changelog tar
    Affected if Using Fedora 35, 36, or 37 with tar processing that could handle specially crafted archives
  5. Check system tar utilities on OpenEuler
    On OpenEuler systems, verify: rpm -q tar and review: rpm -q --changelog tar
    Affected if Running OpenEuler 20.03 or 22.03 with tar processing capabilities
  6. Test for vulnerable code path
    If source code is available, search for malloc calls on gnu_longlink without size validation: grep -n 'gnu_longlink.*malloc\|malloc.*gnu_longlink' source_files.c
    Affected if Code shows malloc called on gnu_longlink without prior validation of the size field being non-zero

Your environment is affected if you have libtar version less than 1.2.21 installed, or are running Fedora 35/36/37 or OpenEuler 20.03/22.03 with tar processing that could handle user-supplied tar archives without prior size validation.

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
Upgrade available Upgrade to 1.2.21 or later
Fixed in 1.2.21
Interim mitigation

Update the tar processing library/code to validate the size field in tar headers before allocating memory, rejecting or properly handling archives with zero-size headers to prevent the malloc(0) call.

Recommended fix High confidence

libtar >= 1.2.21

  1. 1. Identify the libtar package installed on your system using your package manager (e.g., 'rpm -qa | grep libtar' or 'dpkg -l | grep libtar')
  2. 2. Check the currently installed version of libtar
  3. 3. Upgrade libtar to version 1.2.21 or later: On Fedora, run 'dnf update libtar' or 'dnf upgrade libtar'
  4. 4. If you have applications that statically link against libtar, rebuild them after the upgrade to ensure they use the fixed library version
  5. 5. Verify the new version is installed correctly by checking 'rpm -q libtar' or equivalent

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

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2021-33643 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