You can also redirect the output to a text file for archiving: utmpdump /var/run/utmp > utmp.logĭoing the above will give you an output like below: sandflysecurity# utmpdump /var/log/wtmp The utmpdump command is this: utmpdump /var/run/utmp In the most basic form, utmpdump allows us to quickly dump the logs and save them for later review as text.
In order to read them you will need a utility like utmpdump. The utmp, wtmp and btmp files are a binary format. In this post, we’ll be doing our investigation on a Raspberry Pi device running a version of the Raspbian OS which is a Debian variant. It is effectively wiped and recovery of the entry is not possible. The basic thing to know is that when an attacker overwrites an entry with nulls (zeroes), the entry will not show anything about what was there. In this post we’ll cover the first technique and will talk about the second in the future. Remove the suspicious entries and splice the log back together cleanly. Overwrite the suspicious entries with nulls. Aside from simply obliterating the contents, there are two basic ways to alter these files with the log cleaners commonly found: However, more sophisticated attackers will make an attempt to clean the logs. This is a very ham-fisted way to cover your tracks and is easily spotted. Many pieces of Linux malware will simply erase the files and replace them with ones that are zero bytes long.
var/log/btmp – Contains all bad login attempts.īecause the utmp, wtmp and btmp files contain login information about all users, they are prime targets by intruders and malware on Linux to either destroy or alter. var/log/wtmp – Contains all current and past logins and additional information about system reboots, etc. var/run/utmp – Contains currently logged in users. To start, utmpdump is a utility to dump the system audit logs called utmp, wtmp, and btmp. Seemingly unknown by many, the utmpdump command is a great tool for Linux forensics and detecting log file tampering. In this post we’re going to show you how to use utmpdump for investigating Linux audit logs for signs of compromise.
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