Detecting world writable files and directories

Group and world writable files and directories particularly system files partitions, can be a security hole if a cracker gains access to your system and modifies them. Additionally, world-writable directories are dangerous, since they allow a cracker to add or delete files as he or she wishes in these directories. In the normal course of operation, several files will be writable, including some from the /dev, /var/catman  directories, and all symbolic links on your system. To locate all group & world-writable files on your system, use the command:

find / -type f \( -perm -2 -o -perm -20 \) -exec ls -lg {} \;

# find / -type d \( -perm -2 -o -perm -20 \) -exec ls -ldg {} \;

General filesystem security rules related to world-writable files are very simple and can be formulated as following:

• World writable directories (public directories such as /tmp) should have sticky attribute assigned to them.
• No world-writable dot files.
• No world-writable files owned by root.
• Proper mounting attibutes
• No abandoned "nouser/nogroup" files.

So the following probably will be a more smooth way to proceed:

1. Find all files that have such attributes, excluding those in /tmp, /proc and other pseudo-filesystems. The simplest way to do it would probably be via pipes:
2. Create the new list of "abnormal" files using find
3. concat it with the old list
4. sort it
5. do uniq with count option (-c)
6. select those records that have prefix 1

   Something like

   find . -perm -o=w -type f -xdev > /root/new.lst
   cat /root/old.lst /root/new.lst | sort | uniq -c | grep -v ' 2 ' \
      | tee /root/delta_worldwritable_files`/usr/bin/date +%Y%m%d` \
      | mail -s "New worldwritable files at $HOSTNAME"  $primary_admin
   mv /root/old.lst status`/usr/bin/date +%Y%m%d`
   cp /root/new.lst /root/old.lst

   It probably would be better to use diff instead of this trick with sort | uniq

   for part in `awk '($4 == "ufs") {print $3 }' /etc/vfstab` ; do 
       find $part -perm +o=w -type f -xdev -exec ls -l ';' 
   done

7. Compare findings with prev status for the server (for example using diff) and create alerts for any new files found.

8. [Optional] Reset permissions on all world-writable dot files, suid/sgid files and those files that are located in the root directory ( I am trying to enforce moving root account to /root directory on our severs but we are not here yet) as well as in /opt and /usr subtrees (you can modify those recommendations based on your understanding of the environment).

Recommended Links

• Finding World Writable, Abandoned and other Abnormal Files
• Additional means of controlling tree traversal

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Last modified: March 12, 2019