CVE-2021-35939

It was found that the fix for CVE-2017-7500 and CVE-2017-7501 was incomplete: the check was only implemented for the parent directory of the file to be created. A local unprivileged user who owns another ancestor directory could potentially use this flaw to gain root privileges. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

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

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.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/132.html
• https://cwe.mitre.org/data/definitions/17.html
• https://cwe.mitre.org/data/definitions/35.html
• https://cwe.mitre.org/data/definitions/76.html

References

• https://access.redhat.com/security/cve/CVE-2021-35939
• https://bugzilla.redhat.com/show_bug.cgi?id=1964129
• https://github.com/rpm-software-management/rpm/commit/96ec957e281220f8e137a2d5eb23b83a6377d556
• https://github.com/rpm-software-management/rpm/pull/1919
• https://rpm.org/wiki/Releases/4.18.0
• https://security.gentoo.org/glsa/202210-22