CVE-2021-23240

selinux_edit_copy_tfiles in sudoedit in Sudo before 1.9.5 allows a local unprivileged user to gain file ownership and escalate privileges by replacing a temporary file with a symlink to an arbitrary file target. This affects SELinux RBAC support in permissive mode. Machines without SELinux are not vulnerable.

Weakness

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Affected Software

Name	Vendor	Start Version	End Version
Sudo	Sudo_project	*	1.8.32 (excluding)
Sudo	Sudo_project	1.9.0 (including)	1.9.5 (excluding)
Red Hat Enterprise Linux 8	RedHat	sudo-0:1.8.29-7.el8	*
Sudo	Ubuntu	bionic	*
Sudo	Ubuntu	esm-infra/xenial	*
Sudo	Ubuntu	groovy	*
Sudo	Ubuntu	hirsute	*
Sudo	Ubuntu	precise/esm	*
Sudo	Ubuntu	trusty	*
Sudo	Ubuntu	trusty/esm	*
Sudo	Ubuntu	upstream	*
Sudo	Ubuntu	xenial	*

Potential Mitigations

Follow the principle of least privilege when assigning access rights to entities in a software system.
Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

NVD	https://nvd.nist.gov/vuln/detail/CVE-2021-23240
CWE	https://cwe.mitre.org/data/definitions/59.html

Improper Link Resolution Before File Access ('Link Following')

Weakness

Affected Software

Potential Mitigations

References

CVE-2021-23240

Improper Link Resolution Before File Access ('Link Following')

Weakness

Affected Software

Potential Mitigations

Related Attack Patterns

References