Ubuntu Overlayfs Local Privilege Escalation
Posted on 03 December 2021
This Metasploit module exploits a vulnerability in Ubuntu's implementation of overlayfs. The vulnerability is the result of failing to verify the ability of a user to set the attributes in a running executable. Specifically, when Overlayfs sends the set attributes data to the underlying file system via vfs_setxattr, it fails to first verify the data by calling cap_convert_nscap. This vulnerability was patched by moving the call to cap_convert_nscap into the vfs_setxattr function that sets the attribute, forcing verification every time the vfs_setxattr is called rather than trusting the data was already verified.
