CVE-2019-11503

snap-confine as included in snapd before 2.39 did not guard against symlink races when performing the chdir() to the current working directory of the calling user, aka a cwd restore permission bypass.

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://www.openwall.com/lists/oss-security/2019/04/25/7
• https://github.com/snapcore/snapd/pull/6642
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/6VACEKVQ7UAZ32WO4ZKCFW6YOBSYJ76L/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VPU6APEZHAA7N2AI57OT4J2P7NKHFOLM/
• https://www.openwall.com/lists/oss-security/2019/04/18/4