FIN13 (also tracked as ElephantBeetle and SQUAB SPIDER) is a financially-motivated actor performing targeted intrusions against financial institutions in Mexico and Latin America dating back to 2016. Rather than using commodity malware such as CobaltStrike and some Ransomware-as-a-Service binary, they make heavy use of custom tooling such as webshells to tunnel network traffic before monetising their intrusion through data theft and injection of fraudulent transactions into payment systems. This series of rules covers the custom tools attributed to FIN13 in this Mandiant blog post.
Today’s rule matches strings in the SWEARJAR Java-based webshell.
rule MAL_FIN13_SWEARJAR {
meta:
description = "Matches strings found in SWEARJAR cross-platform backdoor used by FIN13 (AKA: ElephantBeetle, SQUAB SPIDER)"
last_modified = "2024-04-08"
author = "@petermstewart"
DaysofYara = "99/100"
sha256 = "e76e0a692be03fdc5b12483b7e1bd6abd46ad88167cd6b6a88f6185ed58c8841"
sha256 = "2f23224937ac723f58e4036eaf1ee766b95ebcbe5b6a27633b5c0efcd314ce36"
ref = "https://www.mandiant.com/resources/blog/fin13-cybercriminal-mexico"
strings:
$a1 = "org/eclipse/jdt/internal/jarinjarloader/RsrcURLConnection.class"
$a2 = "org/eclipse/jdt/internal/jarinjarloader/RsrcURLStreamHandler.class"
$a3 = "org/eclipse/jdt/internal/jarinjarloader/RsrcURLStreamHandlerFactory.class"
$a4 = "bankcard.class"
condition:
filesize < 20KB and
uint16(0) == 0x4b50 and
all of them
}
Find the rest of my 100DaysofYARA posts here, and the rules themselves on my Github repository.
Cyber Poking 