YARA's Private Strings
YARA supports private strings.
A string can be marked as private by including string modifier "private".
Here is a use case.
This is a rule to detect wannacry malware based on its killswitch (I'm using a screenshot to avoid false positives on this diary entry):
This rule searches for 2 strings: the $mz string and the $domain string.
If they are found, the rule will trigger:
Using option -s, one can see where the strings were found inside a file:
$mz at position 0x00 (that's the start of a PE file), and $domain at position 0x0313DB.
If one declares string $mz as private, like this:
Then string $mz is not reported when option -s is used:
Thus modifier private can be used to hide some strings in YARA's output (or callback).
Personally, I've not had to use string modifier private yet. But it can help communicate which strings are important. For example to blue team members that handle the results of YARA rules you design.
$mz is not imporant here, because it is used as a simple trick to identify PE files. And PE files themselves, can be benign or malicious.
But if one finds a PE file containing the wannacry killswitch domain, then its most likely malicious.
Didier Stevens
Senior handler
Microsoft MVP
blog.DidierStevens.com
Comments
www
Nov 17th 2022
6 months ago
EEW
Nov 17th 2022
6 months ago
qwq
Nov 17th 2022
6 months ago
mashood
Nov 17th 2022
6 months ago
isc.sans.edu
Nov 23rd 2022
6 months ago
isc.sans.edu
Nov 23rd 2022
6 months ago
isc.sans.edu
Dec 3rd 2022
5 months ago
isc.sans.edu
Dec 3rd 2022
5 months ago
<a hreaf="https://technolytical.com/">the social network</a> is described as follows because they respect your privacy and keep your data secure. The social networks are not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go.
<a hreaf="https://technolytical.com/">the social network</a> is not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go. The social networks only collect the minimum amount of information required for the service that they provide. Your personal information is kept private, and is never shared with other companies without your permission
isc.sans.edu
Dec 26th 2022
5 months ago
isc.sans.edu
Dec 26th 2022
5 months ago