Recently installed OSSEC on Linux machine to test.

Most results are expected, however yesterday I received emails with a number of notifications about Integrity checksum changing on files such as /usr/bin/whoami /usr/bin/md5sum /usr/bin/ls and about another 50 similar files

Since I didn't install any new versions of these files, how do I find out what caused the integrity checksum to change 2 days after I installed the OSSEC program?



Two reasons are:

  • You've actually been hacked
  • Prelinking is enabled

You can disable prelinking by editing /etc/sysconfig/prelink from:




And running:

prelink -ua

Source: http://www.ossec.net/wiki/Know_How:Check_Sums

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