NanoCoreRAT Behind an Increase in Tax-Themed Phishing E-mails

It seems every mainstream news event or holiday has an accompanying phishing campaign. Opportunistic actors hoping to capitalize on the public's attention are often seen sending phishing e-mails with themes related to the news or the season.. It happened this last holiday season and will likely continue to occur as long as email is around. Unsurprisingly, as we near the U.S. deadline for filing our income taxes, Palo Alto Networks researchers have seen an increase in phishing emails specifically related to taxes. This blog details some recent trends we have been able to identify. Palo Alto Networks noticed both executable attachments and Microsoft Word documents with macros designed to download and execute files. Tax-Themed Phishing Looking through recent email attachments determined to be malicious by WildFire, we noticed a trend in subject lines involving tax forms using the keywords ‘report’, ‘tax’, ‘secure’ and ‘pin’. Pivoting from subject lines to the hash values and filenames of attachments included in the emails allowed us to expand our initial sample set. Finally, using the AutoFocus API and a bit of Python we were able to collect data about the samples included in the tax-themed phishing and build a data frame for further analysis. Within the final sample set, we were able to identify 70 unique malware samples distributed through 2,062 email sessions between September 2, 2015 and January 28, 2016. As expected, email sender addresses were often spoofed to provide a sense of legitimacy. Some examples of email sender addresses: 2015-autax-return@ato.gov.au 2015Refund@cra-arc.gc.ca 2015autaxreturn@ato.gov.au 2015tax-return@irs.gov 2015taxreturn-noreply@irs.gov 2015taxreturn@iras.gov.sg We also noticed the source IP address of the emails primarily came from a free mail service called mail2world. The top 5 source IP addresses by session count were: 209.67.128.221 934 sessions 117.120.5.194 214 sessions 209.67.128.182 213 sessions 23.235.221.158 63 sessions 130.194.13.86 53 sessions While some of the phishing email attachments were PE files, others were MS Word documents with malicious macros. One sample (119f3dd48e316f77974a7ec84c0fdecd943ceed77c30db9a6df0c1b0615b0ac0) included instructions on how to enable macros. Using open source tools, the obfuscated file download functionality is easily located in the Word macro. Looking at the malware contained in each email attachment, the payloads consisted predominantly of NanoCoreRAT or a generic macro downloader that would then download and execute NanoCoreRAT. The countries receiving these phishing messages align with what are believed to be country code indicators in malicious URLs and email attachment names. Recipients of Tax-Based Phishing E-mails Analyzing the malicious macro documents we observed for these tax-themed phishing attacks revealed that although there were a large number of unique samples, their behavior and infrastructure contained significant overlap. In the above figure, we can easily see that six domains were in heavy use by most samples. Second-stage download: www.cnw-inc[.]com www.iphonetechie[.]com NanoCoreRAT Command and Control: dawood01.ddns[.]net dawood02.no-ip[.]org dawood00.no-ip[.]org NanoCore NanoCore is a commodity trojan developed in the .NET framework. According to Symantec, a fully cracked version of NanoCore 1.2.2.0 with premium plugins was released around March 2015 and has been seen targeting the energy sector. This release caused NanoCore to become increasingly popular with adversaries, especially the more frugal ones. Around April 2015 we observed a rise in activity involving NanoCore. We have observed its incorporation into tax-themed phishing since June 2015 and are continuing to see a general increase in activity since then. Below shows the upward trend Palo Alto Networks has seen in NanoCoreRAT being distributed since September 2014. NanoCore is a modular RAT with many of its capabilities provided through plugins. Capabilities provided by the premium plugins we could identify include: keylogging and password "recovery" "stress testing" or DoS download, execute, or install other software remote CLI and UI registry editing socks proxy firewall modification webcam and audio controls The plugins available to a NanoCoreRAT sample are encrypted and stored in the resource section of the PE file. Using dnSpy as a debugger, we extracted the plugins included in sample 758f255abc102d53b7a4e8a8902da57076db9889cb80e81e8f1a344056f00c59 by setting breakpoints on all Assembly.Load calls, running the sample, and manually dumping the raw assembly bytes passed to those functions to disk as DLLs. Most of the plugins included in this sample were obfuscated with Eazfuscater.NET 3.3 and easily deobfuscated using de4dot. NanoCoreRAT uses a custom TCP protocol to connect to a server specified by the attacker on the port of their choosing. Below is the encrypted traffic sent by one sample to 54.152.254.8 on TCP port 4782: 00000000 40 00 00 00 52 5a 31 be 44 a9 01 f5 65 18 54 8e @...RZ1. D...e.T. 00000010 75 be e4 66 6a a4 0f e1 d0 4b 4e 6d 27 b6 19 a1 u..fj... .KNm'... 00000020 0b 21 07 b8 1a 57 60 42 0d 54 d8 4e 1b 04 54 6b .!...W`B .T.N..Tk 00000030 d5 8c 94 a0 76 88 6f 8a 05 88 dc ca 65 62 54 2b ....v.o. ....ebT+ 00000040 fe d4 ab 7c This sample uses DES to encrypt the traffic. It creates DESCryptoServiceProvider with a key from the Assembly Resource Guide Attribute and bytes from the resource section. private static bool smethod_13() { byte[] array = Class8.smethod_16(); if (array != null) { ... Guid guid_ = Class8.smethod_18(Assembly.GetExecutingAssembly()); Class8.byte_2 = Class8.smethod_19(byte_, guid_); Class13.smethod_0(Class8.byte_2); ... } private static Guid smethod_18(Assembly assembly_1) { Guid result = new Guid(((GuidAttribute)assembly_1.GetCustomAttributes(typeof(GuidAttribute), false)[0]).Value); return result; } private static byte[] smethod_19(byte[] byte_3, Guid guid_0) { Rfc2898DeriveBytes rfc2898DeriveBytes = new Rfc2898DeriveBytes(guid_0.ToByteArray(), guid_0.ToByteArray(), 8); return new RijndaelManaged { IV = rfc2898DeriveBytes.GetBytes(16), Key = rfc2898DeriveBytes.GetBytes(16) }.CreateDecryptor().TransformFinalBlock(byte_3, 0, byte_3.Length); } The DES key for this sample is 72 20 18 78 8C 29 48 97, we can use it to decrypt the traffic into the following: 00 00 00 00 12 DD DF 82 E7 AE 59 ED 45 B3 F4 E2 B5 7D 53 A5 EE 0C 14 57 49 4E 2D 48 55 46 44 39 33 41 52 36 32 32 5C 6A 6F 68 6E 0C 07 44 65 66 61 75 6C 74 0C 07 31 2E 32 2E 32 2E 30 .....Ýß‚ç®YíE³ôâµ}S¥î..WIN-HUFD93AR622\john..Default..1.2.2.0 System Guid ComputerName\Username RAT Group Version The bytes are stored in array2 and are encrypted with the following code and stored in the byte array named buffer. byte[] buffer = Class13.icryptoTransform_0.TransformFinalBlock(array2, 0, array2.Length); NanoCore can output messages to a console if the EnableDebugMode parameter is enabled in the RATs configuration. Conclusion Phishing is often how threat attackers gain access to targeted systems and user awareness is the first line of defense. Phishing isn't new but the increased distribution of the full-featured NanoCoreRAT implants is. Users should be made aware of the dangers that enabling macros poses. We have observed macro-based attacks on the rise in October of 2014 Palo Alto Networks customers with WildFire turned on would have been alerted to the presence of this threat on their networks. AutoFocus customers are able to further research both tax-themed phishing and NanoCoreRAT samples and trends. Indicators Email Subject Lines [Attention] Your 2014 Tax Report [Urgent Attention] Your 2015 Secure IP PIN [ATO: URGENT] Your 2014 Tax Return Report! [URGENT ATTENTION] Your 2014 Tax Return! [ATO: ATTENTION] Your 2015 Tax Return PIN! [IRS ATTENTION] Your 2015 Secure IP PIN!!! [HMRC ATTENTION] Your 2015 Tax Report PIN! [ATTENTION] Your 2015 Tax Return PIN!!! Email Attachment Filenames IRSReport.doc CATAXREPORT.doc 2015TaxPIN.pdf.exe [CRA]Report.pdf.exe SGTAXREPORT.doc [CRA]TaxReport.doc [IRS]TaxReport.doc [HMRC]TaxReport.doc TaxReport!!.doc SGTAXREPORT.pdf.exe [CRA]ReadReport.doc UKTaxReturnReport.pdf.exe CATaxReturnReport.pdf.exe [CA]Report.pdf.exe [BE]TaxReport.pdf.exe US2015TaxPIN.doc AUTaxReport.pdf.exe AU2015TaxPIN.doc 2015TaxPIN.doc CRA-Report.doc.exe TaxReport.doc UKTAXREPORT.doc AUTAXREPORT.doc CATaxreturn.doc [CRA]Report!.pdf.exe FRTaxReport.pdf.exe Email Attachment SHA256s b633e5b9d6961f63dbf07ccd864903948a3c0772f2f66f86ad42c5b1faa0c539 a1bc606d12db420c511ba94f042021d34d84ba98a16c016445632ed03d37f909 bbbc92b4ebab54a3b7e35168a0e89ecbae701d3a04ea0df9bb5c132fcb8fa2aa a89dd66865554cbe2b1ea6ff18653e964ac48ef585458d7f2d18f3083d039b39 6c1eb38781214b88cc9f9eb702ad9655f32e033ffa493e0954100b6be9c12d98 4b1b9fa256a6e6473c5ca25ce30ccdb4f955abb5e620d219dce85152d9e440ed d910ffe4bb03c3b0066877b75c8ce5f5bc7ad1ae74908d96f7571bb75bf485f3 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83f29a170ffcb9f13e630e1b240cfb0c75ff6854740ccf700e83af40a2dc770b 677ec33db3d3e9b20894bfc1280d3a9944413434cf4eae844d6f79d49bc372bd 6a8c5e6026e6a5d4561d4006ae7a3f0ab82d5ba4deb21c904684a6c3a5c75a7c 3118ca1232a55ee0d718c5efb2590d3af0a19d6a3861f4c7c56ecf0dcc3a8083 4eca6ea67d389ce85e41804bdb23acd7e34e585b3b92ce521636ffa35d877e32 fc83728faf8ca614e2798d64ed2eca2691354bf83ff5726d52badcd44787db14 87971bb9bdaea061ebea3d6903d6df359a13713e0d5aeda0a3fee0df852c3799 44b6807e0ea21d7f41ca09fa04a8bd1192fd568364a3ac5ba12a7c0de7d57a9d 455705d79026ddfc758cf069267b6975c677e2a28a0f553baca91a3f95d6dbbc 37160143a5064b505f050d8d37fbd2d2492c62afa599c9bbe0a6c5f0e20f3300 d175d0c65acebb61bdefd3e498bb24761c6ffd67c401060649d094e9a7d7753b bf1e3483ec56fb480a88c6208f5ba2e51a69361b8cb26b8002f4c3bc562996fb 73935900282967ad8d1d0822f46c49cd69ae49e15bf63435db5074b6d932ba01 a34a3e1d0e427c9b112bd647fc5b53f1f8401e12bdcf16d6076dbc17fcaa7537 b11ac7fcb5d0427b922a8f6ba0bf6078647cb8bf3bed11ca43dc30f0f30157f2 6335b913b0a900e67155dab585249c1861912116bd53bb46055ee966511f97a8 cdc350df224011bd95f8fc04cfe355b44f1a3732ea7683339227baaa89a7935e 161a7c71330f0088b5bc06cc2a80fb1217e1a834d8ca87e749cdafa64f521bc5 Email Attachment Resolved Domains agor0020.gotdns.ch btint.net16.net dawood00.no-ip.org dawood01.ddns.net dawood02.no-ip.org www.cnw-inc.com www.iphonetechie.com www.pantech224.firstcom.com.sg www.secretchamber.sg NanoCore Deobfuscated Plugin SHA256s ClientPlugin.dll 277f74d0ce633645c1a3a91b45f800f16385496d50c511084ccbd19c33a39b23 CoreClientPlugin.dll 8c18712257e04e0554a4fa8414906489bc4300ee71405719d43ce949decddf18 FileBrowserClient.dll 98b70d6b88b8fdf05d8da676fa7a48622c2d415cd5cf8e8a1f193dc6c65dc101 Lzma#.dll ee05e8bd662e8e59c851b4053d2b34e8524cbe5356ee6c385b07d028a9dfb28d ManagementClientPlugin.dll 3ad61e99f7a09c524121981f536b625fadcb27481d99ffe75938bb550be8883e MyClientPlugin.dll 1e6cc9c0ee28a352611fd1a6b41f4a5e66019729b529d9177b14b25624533cad MyClientPluginNew.dll c986b9e146cb4f88dc68bea7927c76e0056e181b7b0de45fe4a221ce5e900d08 NanoCoreBase.dll ea8ddf633460353ab0e641b97a370873b16ac4aef3e6ef6bffc2c4618256ab64 NanoCoreStressTester.dll edd0e15cdf75f8158c5aae90db3e8c7d7705a247c5d807bc74c027c36ef6dc3d NetworkClientPlugin.dll 6995887a9827808ca41ffbfddbeb93b8de9468387ec8958207a3eb9951d286f6 SecurityClientPlugin.dll ee5cb353a3e4bdce3ac3b514e2e17e0dd0b04d787b4705c7cf1a681c0b422d85 SurveillanceClientPlugin.dll beaf550d664abe4653fd0ddbdd1783894141b51272d8ac565556aa28e2ac847d SurveillanceExClientPlugin.dll 5db139678bcfda1b46ddab1e2956b599da89a364230d16703a4ac0b02325a13a ToolsClientPlugin.dll a4f7a7dddbef1930d11609e4cd7604d1c3a75646db051499b1247b3b03b48692 MyClientPlugin.dll_2 7c1d77c3b41af227c5f6ae49000134420ce9fdd8d3050eceb5aa2358a31a4724 Additional Resources NanoCore and Unpacking the AutoIT Cryptor NanoCore: Another RAT tries to make it out of the gutter

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