Quickpost: PDF/ActiveMime Maldocs YARA Rule

Here is a YARA rule I developed to detect PDF/ActiveMime maldocs I wrote about in “Quickpost: Analysis of PDF/ActiveMime Polyglot Maldocs“.

It looks for files that start with %PDF- (this header can be obfuscated) and contain string QWN0aXZlTWlt (string ActiveMim in BASE64), possibly obfuscated with whitespace characters.

rule rule_pdf_activemime {
    meta:
        author = "Didier Stevens"
        date = "2023/08/29"
        version = "0.0.1"
        samples = "5b677d297fb862c2d223973697479ee53a91d03073b14556f421b3d74f136b9d,098796e1b82c199ad226bff056b6310262b132f6d06930d3c254c57bdf548187,ef59d7038cfd565fd65bae12588810d5361df938244ebad33b71882dcf683058"
        description = "look for files that start with %PDF- and contain BASE64 encoded string …

analysis author base64 characters detect didier didier stevens files header maldocs malware analysis meta obfuscated pdf polyglot quickpost start yara