RansomExx

yara rules

These are a couple of Yara rules that I wrote for detecting RansomExx, a linux-based ransomware.

Usage: $yara ransomexx.yar -path-to-dir-to-be-scanned

Get it from Github

/*
author = "Vishal Thakur - malienist.medium.com"
date = "2021-11-30"
version = "1"
description = "Detects RansomExx Linux Ransomware"
info = "Generated from information extracted from the malware sample by manual analysis."
*/
rule ransomexxStatic {   
  strings:
    $header = { 7f 45 4c 46 02 }
    $email = { 66 72 61 6e 63 65 2e 65 69 67 73 40 70 72 6f 74 6f 6e 6d 61 69 6c 2e 63 6f 6d }
    $msg1 = { 53 74 75 64 79 20 74 68 69 73 20 6d 65 73 73 61 67 65 20 52 45 47 41 52 44 46 55 4c 4c 59 20 61 6e 64 20 63 61 6c 6c 20 61 64 6d 69 6e 69 73 74 72 61 74 6f 72 20 66 72 6f 6d 20 74 65 63 68 6e 69 63 61 6c 20 64 69 76 69 73 69 6f 6e }
    $msg2 = { 45 6e 63 72 79 70 74 65 64 20 66 69 6c 65 20 4d 55 53 54 20 4e 4f 54 20 68 61 76 65 20 72 69 63 68 20 64 61 74 61 }
    $msg3 = { 52 65 61 63 68 20 75 73 20 53 4f 4c 45 4c 59 20 69 66 20 79 6f 75 20 72 65 70 72 65 73 65 6e 74 20 61 6c 6c 20 61 66 66 65 63 74 65 64 20 6e 65 74 77 6f 72 6b }
    $msg4 = { 47 72 65 65 74 69 6e 67 73 20 45 49 47 53 49 }
    $msg5 = { 62 72 61 69 6e 70 6f 6f 6c }
    $msg6 = { 6d 62 65 64 74 6c 73 5f 61 65 73 5f 78 74 73 5f 64 65 63 6f 64 65 5f 6b 65 79 73 }
condition:
    filesize < 270KB and 
    all of them
}
rule ransomexxCode {
  strings:
    $block1 = { ?? 65 6d 6f 76 65 00 6f 70 65 6e 64 69 72 00 61 6c 61 ?? 6d 00 75 73 6c 65 65 70 00 66 77 72 69 74 65 00 66 72 65 61 64 00 67 65 74 74 69 6d 65 6f 66 64 61 79 00 72 65 6e 61 6d 65 00 72 65 61 64 64 69 72 36 34 00 5f 5f 63 78 61 5f 66 69 6e 61 6c 69 7a 65 00 73 79 73 63 61 6c 6c 00 6d 65 6d 6d 6f 76 65 00 66 6f 70 65 6e 36 34 00 73 74 ?? 63 6d 70 00 5f 5f 6c 69 62 63 5f 73 74 61 72 74 5f 6d 61 69 6e 00 66 65 ?? ?? 6f ?? 00 73 6e 70 72 69 6e 74 66 00 73 79 73 63 6f 6e 66 00 66 72 65 65 00 5f 5f 78 73 74 61 74 36 34 00 6c 69 62 70 74 68 72 65 61 64 2e 73 6f 2e 30 00 6c 69 62 63 2e 73 6f 2e 36 00 47 4c 49 42 43 5f 32 2e 32 2e 35 00 47 4c 49 42 43 5f 32 2e 33 2e 34 00 5f 5f 67 6d 6f 6e 5f 73 74 61 72 74 5f  5f }
    $block2 = { ?? 54 4d 5f 64 65 ?? 65 67 69 73 74 65 ?? 54 4d 43 6c 6f 6e 65 54 61 62 6c 65 00 5f 49 54 4d 5f 72 65 67 69 73 74 65 72 54 4d 43 6c 6f 6e 65 54 61 62 6c 65 00 5f 5f 65 72 72 6e 6f 5f 6c 6f 63 61 74 69 6f 6e 00 70 74 68 72 65 61 64 5f 63 72 65 61 74 65 00 70 74 68 72 65 61 64 5f 6d 75 74 65 78 5f 6c 6f 63 6b 00 70 74 68 ?? 65 61 64 5f 6d 75 74 65 78 5f 75 6e 6c 6f 63 6b 00 73 ?? ?? 63 70 79 00 67 6d 74 69 6d 65 5f ?? 00 73 70 72 69 6e 74 66 00 73 72 61 6e 64 00 63 6c 6f 73 65 64 69 72 00 66 74 65 6c 6c 00 73 69 67 6e 61 6c 00 70 75 74 73 00 74 69 6d 65 00 70 75 74 63 68 61 72 00 66 67 65 74 73 00 73 63 68 65 64 5f 73 65 74 61 66 66 69 6e 69 74 79 00 63 61 6c 6c 6f 63 00 73 74 ?? 6c 65 6e 00 6d 65 6d 73 65 74 00 73 74 72 73 74 ?? 00 66 73 65 65 6b 00 6d 65 6d 63 6d 70 00 6d 65 6d 63 70 79 00 66 63 6c 6f 73 65 00 6d 61 6c 6c 6f 63 00 73 74 ?? 63 61 }
  condition:
    filesize < 270KB and 
    all of them
}