module

2021 Ubuntu Overlayfs LPE

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Disclosed
2021-04-12
Created
2021-12-08

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.

Authors

ssd-disclosure
bwatters-r7

Platform

Linux

References

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_overlayfs
    msf exploit(cve_2021_3493_overlayfs) > show targets
        ...targets...
    msf exploit(cve_2021_3493_overlayfs) > set TARGET < target-id >
    msf exploit(cve_2021_3493_overlayfs) > show options
        ...show and set options...
    msf exploit(cve_2021_3493_overlayfs) > exploit
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