YARA's BASE64 Strings
Since YARA version 4.0.0, Victor added support for detecting BASE64 encoded strings.
This means that from version 4.0.0 you can write a rule to search for strings that are BASE64 encoded.
For example, looking for string "Internet Storm Center" in BASE64 encoding, means searching for SW50ZXJuZXQgU3Rvcm0gQ2VudGVy (or other, depending on the position).
A rule for this string would look like this:
rule base64_ascii_ascii {
strings:
$a = "Internet Storm Center" base64
condition:
$a
}
This rule looks for ASCII strings that are valid BASE64 strings, and that decode to ASCII string "Internet Storm Center".
When you use keyword base64, you search for ASCII BASE64 strings. You can also search for UNICODE BASE64 strings, using keyword base64wide.
But in both cases, the decoded string is an ASCII string. If the decoded string has to be a UNICODE string, you need to use keyword wide.
Here are 4 YARA rules, illustrating the 4 different combinations (ASCII ASCII, UNICODE ASCII,, ASCII UNICODE, and UNICODE UNICODE):
rule base64_ascii_ascii {
strings:
$a = "Internet Storm Center" ascii base64
condition:
$a
}rule base64_unicode_ascii {
strings:
$a = "Internet Storm Center" wide base64
condition:
$a
}rule base64_ascii_unicode {
strings:
$a = "Internet Storm Center" ascii base64wide
condition:
$a
}rule base64_unicode_unicode {
strings:
$a = "Internet Storm Center" wide base64wide
condition:
$a
}
If you don't know what combination you are looking for, you can also use the following rule that will match all combinations:
rule base64_all {
strings:
$a = "Internet Storm Center" ascii wide base64 base64wide
condition:
$a
}
Example:
Didier Stevens
Senior handler
Microsoft MVP
blog.DidierStevens.com DidierStevensLabs.com
Comments
www
Nov 17th 2022
4 months ago
EEW
Nov 17th 2022
4 months ago
qwq
Nov 17th 2022
4 months ago
mashood
Nov 17th 2022
4 months ago
isc.sans.edu
Nov 23rd 2022
3 months ago
isc.sans.edu
Nov 23rd 2022
3 months ago
isc.sans.edu
Dec 3rd 2022
3 months ago
isc.sans.edu
Dec 3rd 2022
3 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
2 months ago
isc.sans.edu
Dec 26th 2022
2 months ago