Privilege escalation in GNU Bash

1) Improper Check for Dropped Privileges

EUVDB-ID: #VU24690

Risk: Low

CVSSv4.0: 7.1 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P/U:Clear]

CVE-ID: CVE-2019-18276

CWE-ID: CWE-273 - Improper Check for Dropped Privileges

Exploit availability: Yes

Description

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

The vulnerability exists in "disable_priv_mode()" function in shell.c due to the affected software attempts to drop privileges but does not check or incorrectly checks to see if the drop succeeded. A local user with command execution in the shell can use "enable -f" for runtime loading of a new builtin, which can be a shared object that calls setuid() and therefore regains privileges.

Mitigation

Cybersecurity Help is currently unaware of any official solution to address this vulnerability.

Vulnerable software versions

Bash: 5.0 patch 1 - 5.0

CPE2.3

• cpe:2.3:a:gnu:bash:5.0 patch 1:*:*:*:*:*:*:*
• cpe:2.3:a:gnu:bash:5.0 patch 2:*:*:*:*:*:*:*
• cpe:2.3:a:gnu:bash:5.0 patch 3:*:*:*:*:*:*:*

External links

https://packetstormsecurity.com/files/155498/Bash-5.0-Patch-11-Privilege-Escalation.html
https://github.com/bminor/bash/commit/951bdaad7a18cc0dc1036bba86b18b90874d39ff
https://www.youtube.com/watch?v=-wGtxJ8opa8

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.