#VU26210 Improper Check for Dropped Privileges in zsh - CVE-2019-20044

Vulnerability identifier: #VU26210

Vulnerability 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-2019-20044

CWE-ID: CWE-273

Exploitation vector: Local

Exploit availability: Yes

Vulnerable software:
zsh
Client/Desktop applications / Software for system administration

Vendor: SourceForge

Description

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

The vulnerability exists due to Zsh fails to overwrite the saved uid, so the original privileges, dropped by the --no-PRIVILEGED option, can be restored by executing MODULE_PATH=/dir/with/module zmodload with a module that calls setuid(). A local user can execute arbitrary commands on the system with elevated privileges.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

zsh: 5.0.0 - 5.7.1

---

External links
https://zsh.sourceforge.net/releases.html
https://github.com/XMB5/zsh-privileged-upgrade
https://lists.debian.org/debian-lts-announce/2020/03/msg00004.html
https://www.zsh.org/mla/zsh-announce/141

---

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.