dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-33645

HIGH · 7.5 CVSS v3.1 Published 2022-08-10
Fix available
A fix is available. Upgrade to 1.2.21 or later.
See remediation →
84/100
Remediation priority · High
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
The th_read() function doesn’t free a variable t->th_buf.gnu_longlink after allocating memory, which may cause a memory leak.

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 memory leak vulnerability exists in the th_read() function where allocated memory for t->th_buf.gnu_longlink is not freed after use. This can lead to resource exhaustion over time, especially in scenarios where the function is called repeatedly.

MitigationEnsure proper deallocation of t->th_buf.gnu_longlink memory in all code paths within the th_read() function, typically by adding a free() call when the buffer is no longer needed.

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
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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 libtar library installation
    Run 'rpm -qa | grep libtar' (Fedora/OpenEuler) or check for libtar.so in /usr/lib/ or /usr/local/lib/
    Affected if libtar version is found and matches < 1.2.21 on Fedora 35/36/37 or OpenEuler 20.03/22.03, or any version < 1.2.21 regardless of distro
  2. Find applications linked to libtar
    Run 'ldconfig -p | grep libtar' or 'find /usr -name "*.so*" -exec ldd {} \; 2>/dev/null | grep libtar' to find linked binaries
    Affected if Any application is dynamically linked to a vulnerable libtar version (< 1.2.21)
  3. Identify if th_read function is exercised
    Check application logs or code if tar archive extraction/processing occurs; the vulnerability triggers when reading GNU-format tar archives with long filename entries
    Affected if Applications using libtar process tar archives, especially those with long filenames (>100 chars) requiring GNU longlink extension
  4. Monitor for memory accumulation
    Run the application with memory profiling tools (valgrind, /usr/bin/time -v) during tar processing tasks and observe if memory usage grows unbounded over repeated operations
    Affected if Memory usage increases continuously without stabilization during repeated tar extraction operations

You are affected if libtar version < 1.2.21 is installed and any application using it processes tar archives, as the unmemory leaked in th_read() will accumulate with each archive processed.

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

Ensure proper deallocation of t->th_buf.gnu_longlink memory in all code paths within the th_read() function, typically by adding a free() call when the buffer is no longer needed.

Recommended fix High confidence

libtar >= 1.2.21

  1. For Fedora systems (35, 36, 37): Run 'sudo dnf update libtar' or 'sudo dnf upgrade libtar' to get the patched version
  2. For systems using libtar source directly: Download libtar version 1.2.21 or later from the official repository (https://github.com/tklauser/libtar)
  3. Recompile and reinstall libtar following standard build procedures (./configure, make, make install)
  4. Rebuild any applications that link against libtar to ensure they use the fixed library
  5. Verify the fix by running applications that use libtar and monitoring memory usage

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

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,900
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,040.

Scan for this in your stack

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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-2021-33645 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