CVE-2019-12209

Yubico pam-u2f 1.0.7 attempts parsing of the configured authfile (default $HOME/.config/Yubico/u2f_keys) as root (unless openasuser was enabled), and does not properly verify that the path lacks symlinks pointing to other files on the system owned by root. If the debug option is enabled in the PAM configuration, part of the file contents of a symlink target will be logged, possibly revealing sensitive information.

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

• http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00012.html
• http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00018.html
• http://www.openwall.com/lists/oss-security/2019/06/05/1
• https://developers.yubico.com/pam-u2f/Release_Notes.html
• https://github.com/Yubico/pam-u2f/commit/7db3386fcdb454e33a3ea30dcfb8e8960d4c3aa3
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5FOR4ADC356JPCHAJI5UXZORLC3VNBPS/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZCGU6UQLI3ZTW3UYCTMQW7VDL5M4LCWR/