---
title: "CVE-2021-33643\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2021-33643?format=md
keywords: index, follow
---

# CVE-2021-33643

Publication date 10 August 2022

Last updated 25 August 2025

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**9.1 · Critical**

[Score breakdown](https://ubuntu.com/security/CVE-2021-33643?format=md#impact-score)

Toggle side navigation

## Description

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.

[Read the notes from the security team](https://ubuntu.com/security/CVE-2021-33643?format=md#notes)

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| libtar | 25.04 plucky | Not in release |
| 24.10 oracular | Fixed 1.2.20-8.1ubuntu0.24.10.1 |
| 24.04 LTS noble | Fixed 1.2.20-8.1ubuntu0.24.04.1 |
| 22.04 LTS jammy | Fixed 1.2.20-8ubuntu0.22.04.1 |
| 20.04 LTS focal | Fixed 1.2.20-8ubuntu0.20.04.1 |
| 18.04 LTS bionic | Fixed 1.2.20-7ubuntu0.1~esm1  Ubuntu Pro |
| 16.04 LTS xenial | Fixed 1.2.20-4ubuntu0.1~esm1  Ubuntu Pro |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)
* [Patch details](https://ubuntu.com/security/CVE-2021-33643?format=md#patch-details)

### Get expanded security coverage with Ubuntu Pro

Reduce your average CVE exposure time from 98 days to 1 day with expanded CVE patching, ten-years security maintenance and optional support for the full stack of open-source applications. Free for personal use.

[Get Ubuntu Pro](https://ubuntu.com/pro)
[30-day free trial](https://ubuntu.com/pro/free-trial)

## Notes

---

### [john-breton](https://launchpad.net/~john-breton)

Upstream never released a patch, but a third-party patch
exists from OpenEuler. The patch fixes CVE-2021-33643
and CVE-2021-33644.

### Patch details

For informational purposes only. We recommend not to cherry-pick updates. [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)

| Package | Patch details |
| --- | --- |
| libtar | * Vendor:   <https://gitee.com/src-openeuler/libtar/blob/master/openEuler-CVE-2021-33643-CVE-2021-33644.patch> |

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

9.1 · Critical

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | High |
  | Integrity impact | None |
  | Availability impact | High |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 9.1 · Critical |
  | Exploitability score | - |
  | Impact score | - |

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

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-33643)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2021-33643)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2021-33643)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2021-33643)

### Related Ubuntu Security Notices (USN)

+ [USN-7398-1](https://usn.ubuntu.com/USN-7398-1)
+ libtar vulnerabilities
+ 31 March 2025

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2021-33643>
* <https://bugzilla.redhat.com/show_bug.cgi?id=2121289>