dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-33644

HIGH · 8.1 CVSS v3.1 Published 2022-08-10
Fix available
A fix is available. Upgrade to 1.2.21 or later.
See remediation →
88/100
Remediation priority · High
Remotely reachable No privileges

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_longname, 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

This is an out-of-bounds read vulnerability in tar file parsing. When a crafted tar file has a size value of 0 in the header struct, the code calls malloc(0) for the gnu_longname variable, which may return a valid pointer to a zero-byte allocation. Subsequent read operations from this pointer cause out-of-bounds memory access.

MitigationImplement validation to check the size field in tar headers before memory allocation, and add proper error handling for the malloc(0) case to prevent out-of-bounds access.

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 the Linux distribution and version
    Run 'cat /etc/os-release' or 'hostnamectl' to determine the distribution and version
    Affected if The system runs Fedora 35, 36, or 37, or OpenEuler 20.03 or 22.03
  2. Check if libtar library is installed
    Run 'rpm -qa | grep libtar' or check for libtar.so in /usr/lib/ or /usr/lib64/
    Affected if libtar version is found to be less than 1.2.21 (run 'rpm -qi libtar' for version details)
  3. Identify applications using libtar for tar parsing
    Search for binaries or libraries that link to libtar using 'ldd <binary>' or 'nm -D <library>' | grep tar_
    Affected if An application dynamically links to libtar and processes untrusted tar files
  4. Verify tar processing code path in custom applications
    Review application source code or binary for calls to tar_open, tar_extract, or similar libtar functions that parse tar headers
    Affected if The application uses libtar to parse tar files where a crafted tar with size=0 in header could be processed
  5. Check for affected tar handling in downstream products
    If using a product built on Fedora or OpenEuler that includes tar parsing functionality, verify the libtar version bundled or shipped
    Affected if The bundled libtar version is below 1.2.21

The environment is affected if it runs Fedora 35/36/37 or OpenEuler 20.03/22.03 with libtar version below 1.2.21, and processes untrusted tar files using the vulnerable code path.

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

Implement validation to check the size field in tar headers before memory allocation, and add proper error handling for the malloc(0) case to prevent out-of-bounds access.

Recommended fix High confidence

libtar >= 1.2.21; Fedora 35/36/37 to latest available update containing the fix; OpenEuler 20.03/22.03 to latest available update containing the fix

  1. Identify the libtar package installed on the system using package manager (e.g., dnf for Fedora, yum for OpenEuler)
  2. Update the libtar package to version 1.2.21 or later using: `dnf update libtar` (Fedora) or `yum update libtar` (OpenEuler)
  3. Verify the updated version using: `rpm -q libtar`
  4. Restart any services or applications that use libtar to ensure the patched library is loaded
Caveat Library minor version upgrade typically has low risk of breaking changes; however, test applications that depend on libtar after applying the update

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-2021-33644 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