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Vulnerability of BusyBox: directory traversal of tar

Synthesis of the vulnerability 

An attacker can create a malicious tar archive, to traverse directories in BusyBox, in order to create a file outside the service root path.
Impacted systems: BusyBox, Debian, Ubuntu.
Severity of this alert: 2/4.
Creation date: 22/10/2015.
Références of this alert: 8411, CVE-2011-5325, DLA-1445-1, DLA-1445-2, DLA-1445-3, DLA-2559-1, USN-3935-1, VIGILANCE-VUL-18155.

Description of the vulnerability 

The BusyBox product can extract archives in tar format.

However, if the archive contains a symbolic link to a directory, the archival/tar.c file of BusyBox accepts to follow this link, and to create files outside the working directory.

An attacker can therefore create a malicious tar archive, to traverse directories in BusyBox, in order to create a file outside the service root path.
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This computer threat bulletin impacts software or systems such as BusyBox, Debian, Ubuntu.

Our Vigil@nce team determined that the severity of this security threat is medium.

The trust level is of type confirmed by the editor, with an origin of internet client.

A proof of concept or an attack tool is available, so your teams have to process this alert. An attacker with a technician ability can exploit this computer vulnerability alert.

Solutions for this threat 

BusyBox: workaround for tar.
A workaround is to not open tar archives from unknown sources.

Debian 8: new busybox packages.
New packages are available:
  Debian 8: busybox 1:1.22.0-9+deb8u4

Debian 9: new busybox packages.
New packages are available:
  Debian 9: busybox 1:1.22.0-19+deb9u1

Ubuntu: new busybox packages.
New packages are available:
  Ubuntu 18.10: busybox 1:1.27.2-2ubuntu4.1
  Ubuntu 18.04 LTS: busybox 1:1.27.2-2ubuntu3.2
  Ubuntu 16.04 LTS: busybox 1:1.22.0-15ubuntu1.4
  Ubuntu 14.04 LTS: busybox 1:1.21.0-1ubuntu1.4
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