Advent Of Cyber 3 - Day 21

Posted on Dec 21, 2021
tl;dr: Yara

When analyzing files, it can be handy to verify them agains a couple of antivirus engines as well as other available tools that can analyze the behaviour.

Yara is a tool where the community can commit rules they’ve created for known malware, which helps the blueteam to know what to look for.

recommended github repo: awesome-yara

recommended THM room for playing around with yara more: yara-room

todays challenge

We changed the text in the string $a as shown in the eicaryara rule we wrote, from X5O to X50, that is, we replaced the letter O with the number 0. The condition for the Yara rule is $a and $b and $c and $d. If we are to only make a change to the first boolean operator in this condition, what boolean operator shall we replace the ‘and’ with, in order for the rule to still hit the file?

answer: or

What option is used in the Yara command in order to list down the metadata of the rules that are a hit to a file?

answer: -m

What section contains information about the author of the Yara rule? answer: metadata

What option is used to print only rules that did not hit? answer: -n

Change the Yara rule value for the $a string to X50. Rerun the command, but this time with the -c option. What is the result?

answer: 0