Description
This 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.
Module options
To display the available options, load the module within the Metasploit console and run the commands 'show options' or 'show advanced':
msf > use exploit/linux/local/cve/2021_3493_overlayfsmsf undefined(2021_3493_overlayfs) > show actions ...actions...msf undefined(2021_3493_overlayfs) > set ACTION < action-name >msf undefined(2021_3493_overlayfs) > show options ...show and set options...msf undefined(2021_3493_overlayfs) > runPrioritise with Active Threat Intelligence
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