CVE-2019-20044

In Zsh before 5.8, attackers able to execute commands can regain privileges dropped by the –no-PRIVILEGED option. Zsh fails to overwrite the saved uid, so the original privileges can be restored by executing MODULE_PATH=/dir/with/module zmodload with a module that calls setuid().

Weakness

The product attempts to drop privileges but does not check or incorrectly checks to see if the drop succeeded.

Affected Software

Name	Vendor	Start Version	End Version
Zsh	Zsh	*	5.8 (excluding)
Red Hat Enterprise Linux 6	RedHat	zsh-0:4.3.11-11.el6_10	*
Red Hat Enterprise Linux 7	RedHat	zsh-0:5.0.2-34.el7_7.2	*
Red Hat Enterprise Linux 8	RedHat	zsh-0:5.5.1-6.el8_1.2	*
Red Hat Enterprise Linux 8	RedHat	zsh-0:5.5.1-6.el8_1.2	*
Red Hat Enterprise Linux 8.0 Update Services for SAP Solutions	RedHat	zsh-0:5.5.1-6.el8_0.2	*
Zsh	Ubuntu	bionic	*
Zsh	Ubuntu	eoan	*
Zsh	Ubuntu	esm-infra/bionic	*
Zsh	Ubuntu	esm-infra/xenial	*
Zsh	Ubuntu	trusty	*
Zsh	Ubuntu	upstream	*
Zsh	Ubuntu	xenial	*

Potential Mitigations

Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

NVD	https://nvd.nist.gov/vuln/detail/CVE-2019-20044
CWE	https://cwe.mitre.org/data/definitions/273.html

Improper Check for Dropped Privileges

Weakness

Affected Software

Potential Mitigations

References