AN ANALYSIS REPORT OF BLACKMAILER TROJAN SPREAD BY EMAILING JS SCRIPT
An Analysis Report of Blackmailer Trojan Spread by Emailing JS Script
By Antiy PTA Group
First draft: December 4, 2015, 11: 11
A new blackmailer variant email with new transmission characters was captured by Antiy Threat Situational Awareness System on December 2, 2015, which was guided by a JS script in compressed package rather than spread by sending binary file load directly.
Antiy PTA group has made an analysis of related incidents and samples. This sample is TeslaCrypt 2.x, a variant of TeslaCrypt. A zip file near to the mail is unzipped to a JS script. After JS script is executed, it will download TeslaCrypt2.x to run, traverse computer files and encrypt 186 kinds of suffix format files, including documents, pictures, audio and etc. After the encryption, it will open blackmailer’s homepage to blackmail and ask for 500 USD to decrypt within a specified time. If overdue, 1000 USD is needed. As TeslaCrypt2. X variant changing the way of key calculation with the ECDH algorithm, hackers and victims can negotiate a key without sharing any secret. TeslaCrypt decryption tool released by Cisco  has been unable to decrypt.
TeslaCrypt2.x spreads by sending plenty of emails, one screenshot of an email is as follows:
It uses “Hello” to address rather than a specific name. The text body is “Please check the attachment, E-mail documents will be mailed to you and this electronic version is sent to you for your convenience “. In order to show the importance of this email, blackmailer emphasizes that the mail is sending by a traditional way.Thus, the recipient may regard it as an important one and check the attachment.
E-mail attachment is invoice_06796407.zip, unzipped as INVOICE_main_BD3847636213. js file which is a downloader used to download TeslaCrypt 2. X and execute.
|Virus name||Torjan/ js .Downloader.gen|
|Original file name||INVOICE_main_BD3847636213. js|
|Size||6.48KB (6,644 bytes)|
|VT first update time||2015-12-02|
|VT detect result||23/52|
INVOICE_main_BD3847636213. js adopts transformed encryption to avoid antivirus detection, which can self-decrypted by Eval function to obtain clear code. When user double-clicks this JS file, it will download executable files from three network addresses orderly to the Temp directory and execute them. If downloads and runs successfully in the first address, the following two addresses will not download. The network address is divided by space:
The content contrast of relevant code before and after decryption is as follows:
This variant is similar to previous malicious act in Tesla report and can take another security team IsightPartners’s report for reference . After the samples being executed, it will AES256 encrypt the document, save the recovery file required information to the registry and text files and sends related information to Tor server controlled by hacker.
|Original file name||76.exe|
|Size||391.0 KB (400,384 bytes)|
|Compiled language||Microsoft Visual C++ 9.0|
|VT first update time||2015-12-03|
|V T detect result||25/52|
Samples uses junk instruction and debugging techniques and starts by hanging to read their own data and rewrite to a new hang after decryption process, and determines whether their own path is the specified Application Data file path. If not, it will move to this directory and modify the file name as a random five letters -a.exe, (such as mghsd-a.exe). With creating a fixed mutex value “78456214324124”, PTA found it adopted bcedit disabled security mode and recovery mode in dynamic analysis environment. It creates a startup in the registry:
Then, it creates multiple working threats, analysis of some key threats is as follows:
(1) Delete volume shadow copy in system，exe delete shadows /all /Quiet
(2) Start threat traverse process path, if the path concludes any string of Taskmgr、procexp、regedit、msconfig、ex, end related process. Thus, CMD, task manager and process check tools cannot open and thus cannot check and end malicious sample process.
(3) Another thread is mainly used to connect to the Internet to report information to hackers controlling server, the connected URLs mainly include:
Visit myexternalip.com/raw to acquire outer network IP information of victim host.
Submit information by visiting following network addresses:
Table3‑1 Domain names of visiting network
Most files are Get request connection PHP files, parameter formats of the request and data of one request are as follows:
Sub=%s&key=%s&dh=%s&addr=%s&size=%lld&version=%s&OS=%ld&ID=%d&gate=%s&ip=%s&inst_id=%X%X%X%X%X%X%X%X，the data that actually sent is as below:
First, get all disk information on local system. If it is a local disk and network disk, traverse all disk files. When the file name contains recove, . VVV, release directly. If not, detect file extension. If the extension name matches with any of the following one, it starts to maliciously encrypt files:
.r3d .css .fsh .lvl .p12 .rim .vcf.3fr .csv .gdb .m2 .p7b .rofl .vdf.7z .d3dbsp .gho .m3u .p7c .rtf .vfs0.accdb .das .hkdb .m4a .pak .rw2 .vpk.ai .dazip .hkx .map .pdd .rwl .vpp_pc.apk .db0 .hplg .mcmeta .pdf .sav .vtf.arch00 .dba .hvpl .mdb .pef .sb .w3x.arw .dbf .ibank .mdbackup .pem .sid .wb2.asset .dcr .icxs .mddata .pfx .sidd .wma.avi .der .indd .mdf .pkpass .sidn .wmo.bar .desc .itdb .mef .png .sie .wmv.bay .dmp .itl .menu .ppt .sis .wotreplay.bc6 .dng .itm .mlx .pptm .slm .wpd.bc7 .doc .iwd .mov .pptx .snx .wps.big .docm .iwi .mp4 .psd .sql .x3f.bik .docx .jpe .mpqge .psk .sr2 .xf.bkf .dwg .jpeg .mrwref .pst .srf .xlk.bkp .dxg .jpg .ncf .ptx .srw .xls.blob .epk . JS .nrw .py.sum .xlsb.bsa .eps .kdb .ntl .qdf .svg .xlsm.cas .erf .kdc .odb .qic .syncdb .xlsx.cdr .esm .kf .odc .raf .t12 .xxx.cer .ff .layout .odm .rar .t13 .zip.cfr .flv .lbf .odp .raw .tax .ztmp.cr2 .forge .litemod .ods .rb .tor.crt .fos .lrf .odt .re4 .txt.crw .fpk .ltx .orf .rgss3a .upk
Related encryption process and encryption file formats can take Kappa analysis for reference which mainly adopts ECDH algorithm to encrypt the key . Cisco Tesla decryption tool  can decrypt Tesla early varieties, the early varieties can save the key to file “key.bat”. And key generation and save of Tesla2.x variants have changed and will be stored in the registry
HKCU\HKEY_CURRENT_USER\Software\HKEY_CURRENT_USER\Software\7CE14F27E7D3E895， 7CE14F27E7D3E895 is personal identification code, every user is different, which is used by hackers to identify the user on the server. Information stored in the registry is the same as recover_file_*.txt
The encrypted data covers the source file and then modifies the file name. In addition to infect local computer, it will try to enumerate computers in a network and infect encrypted files. When all encryption is completed, it will generate recover_file_ *. txt in the My Documents directory, its content is as follows:
And then, it generates Howto_RESTORE_FILES in the following three formats in user desktop and opens which is used to remind users:
Finally, it will pop up a warning page to prompt blackmailer homepage visiting and key encrypted. And the keys can be got by visiting blackmailer server.
To get the key to decrypt files, you have to pay 500 USD. If payment is overdue, you have to pay 1000 USD.
Antiy technicians found that blackmailer network sever hides in Tor network to avoid tracking. Clicking the page that blackmailer provided is as follows: inputing identification number can prevent automated traverse and query of victim information.
After correlating data, the servers that the following URL point to are the same, which are servers of Tesla (2) x blackmailer variants and the information that queried by the same ID in these three websites is also the same.
Victim IP126.96.36.199, the data that two URLs returned is the same.
If the reported server of blackmailer is blocked by network security equipment, it cannot receive the encrypted information reported, and the query by personal code in this page will prompt login unsuccessful. In order to be able to provide decryption services, blackmailer has designed a function, that is, save recover_file_xxxxx. txt file upload in “My Documents” folder and then the encrypted information can be got. The diagram is below:
Through a correlation of network framework, a decrypted URL program is found, that is http://psbc532jm8c.hsh73cu37n1.net/decrypt.zipMD5：AE3E2206ACB24A60FF583F2CF0C77E59
It also contains PDB information in C:\wrk\decrypt\decrypt\Release\decrypt.pdb. It can be got that public and private key encryption and decryption algorithm of OpenSSL ECDH is used, which also shows that it adopts ECDH key to encrypt files.
Blackmailer can spread executable PE load through email packaged software by double extension, SCR extension skills, etc. In this campaign, it uses JS format’s disguise to avoid detection and prevention of antivirus software. At the same time, Tesla 2. x blackmailer adopts ECDH encryption algorithm and puts user data in danger, rather than previous reverse get key to decrypt files.
From a past monitoring, we found that the victims of blackmailer malware are from the original individual users widely to business users, or even servers. Antiy has strengthened its detection and defense ability of blackmailer Trojan in its PTD system and IEP system.
As the increasing danger of data security threats, enterprise users also need to defense blind area through competency-based products and effectively improve network security awareness, build defense in depth system, and get threat information through threat information platforms timely to reduce further proliferation of risk.
 teslacrypt 2.0伪装cryptowall
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