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        "content": "\n            Provide a detailed analysis of the product security features described in:\n            \n            Content to analyze:\n            Search Free Trial Get Demo Crypter Malware A Deep Dive Into NSIS-Based Crypters March 6, 2022 We have been observing that malware is being distributed via NSIS-based crypter . Malware such as FormBook, AgentTesla, GULoader, just to name a few, have been using NSIS as their loader. We have seen several ways of obfuscation implemented with the installer that decrypts and directly loads the malware into memory without dropping its file to the disk. What is NSIS? A quick overview of NSIS Nullsoft Scriptable Install System it is an open-source script-driven tool that can be used to create Windows software installers. This tool is flexible and can let you bundle several components such as executable files EXE, DLL, configs, etc., together with a script that allows you to control the logic of its installation. Although a lot of legitimate developers are using it, threat actors take advantage of using this to spread malware. In this article, we will re-visit the NSIS-based crypter that we came across in the past couple of years. We will also include an in-depth analysis of a recent NSIS-based crypter variant that we encountered. What is Crypter Malware? A crypter is a specific type of software that has the ability to encrypt, obfuscate, and manipulate different kinds of malware. This makes it harder to detect by security programs. Crypters are used by cybercriminals in order to create malware that bypasses security programs by presenting itself as being a harmless program until it is installed. Types of Crypters A crypter contains a specific crypter stub, which is the code used to encrypt and decrypt forms of malicious code. Depending on the stub the crypter uses, they can be classified as staticstatistical or polymorphic. Staticstatistical crypters utilize stubs to make each encrypted file unique. Having separate stubs for each of these clients makes it easy for malicious actors to modify a stub once it is detected by a security software. Polymorphic crypters are more advanced than static crypters. They use algorithms with random variables, data, keys, decoders, and more. For this reason, one input source file will never produce an output file that is identical to the output of another source file. How Crypters Spread Malicious Code Cybercriminals build or buy crypters on the underground market in order to encrypt malicious programs then reassemble code into an actual working program. They then send these programs as part of an attachment within phishing emails and spammed messages. Unknowing users open the program, which will force the crypter to decrypt itself and then release the malicious code. Crypter Evolution During our continuous monitoring of this crypter , we observed 3 different variants in the past year. Let us take a quick look at the overview of some variants weve seen. Note A NSIS-based installer package is an archive that can be unpacked using 7zip. For each sample, we are going to use the older version of 7zip 15.05 since newer versions do not support the unpacking of NSIS.nsi script used to control the installation tasks. Variant 1 Variant 1 NSIS Package Structure This variant consists of an encrypted payload 9pmuxhk1iu03tej275 and a shellcode kvrgxxmwpsiu, both using random file names. Looking at the script, we see that the shellcode will be copied to newly allocated memory using the kernel32 functions CreateFile and ReadFile. The shellcode will be executed using the Call function exported by System.dll plugin. This shellcode is responsible for decrypting and loading the final payload. Variant 1 NSIS.nsi Code Snippet This variant consists of an encrypted payload 9pmuxhk1iu03tej275 and a shellcode kvrgxxmwpsiu, both using random file names. Looking at the script, we see that the shellcode will be copied to newly allocated memory using the kernel32 functions CreateFile and ReadFile. The shellcode will be executed using the Call function exported by System.dll plugin. This shellcode is responsible for decrypting and loading the final payload. Variant 2 Variant 2 NSIS Package Structure Aside from uninstall.exe, this variant also contains an additional encrypted shellcode splitting its execution into two 2 stages. The first stage shellcode fsbkkvdwiinqth is executed the same way as the first variant, which decrypts the second stage shellcode u58asrazgajcg2qv9. The second stage shellcode eventually decrypts and loads the final malware payload from the encrypted payload 6wgd9oc89v. Variant 3 Variant 3 NSIS Package Structure This variant consists of a custom DLL extension mvbdioqy.dll and encrypted payload jav16vrhevoza7ci1qf0, both making use of random file names. The DLL contains at least 1 exported function which is executed using the CallInstDLL , which is an NSIS scripting instruction used to call a function name inside an NSIS extension DLL. Variant 3 NSIS.nsi Code Snippet A randomly named DLL function, in this case xxsybdzh, is used to decrypt and execute another embedded shell code within the DLL, which is then used to decrypt and load the final malware payload from jav16vrhevoza7ci1qf0. Shellcode Decryption Routine There are other variants of these DLL plugins. Please take note that the decryption algorithm used to decrypt the shellcode varies in different samples. As shown in the image above, the decrypted shellcode is executed as a function call. However, in other variants, the shellcode is executed using Windows API calls, which accept an application-defined function as a parameter, in this case, the parameter is the decrypted shellcode. Shown below is a variant, which uses the Windows API GrayStringA to execute the shellcode third line from the bottom. Execute shellcode through API with application-defined function There are other DLLs that contain multiple exported functions using random function names. It is apparent that this is an attempt to confuse analysts in picking the right function to look at. However, looking through the  NSIS.nsi script will help analysts identify the export function that contains the malicious code. Random Export Function Names Analyzing all the variants mentioned above, the decryption of the final payloads varies with each sample, but malware payload is loaded using a similar method. Analysis Now lets dig deeper on how this NSIS-based cryptor works. We will be using the most recent cryptor variant we have seen, which is utilized by FormBook and AgentTesla malware. Techniques used are not that trivial, but we deem worthy to dig into. NSIS Package Files Extracted NSIS Installer Package The package did not contain any DLL plugins . But we can see that it contains an executable file lzxupx.exe and 2 randomly named files 8yhm36shrfdb7m and mhwrt. Shown below are the contents of these files. Contents of 2 unknown files Lets take a look at the NSIS script NSIS.nsi  and check how these files will be used. As shown in the following code snippet of the NSIS script, we can see that the EXE file will be executed with a parameter pointing to one of the randomly named files line number 92 in the image below. NSIS script snippet EXE Analysis lzxupx.exe Lets look at the behavior of the EXE from the NSIS package. Loading this in IDA Interactive Disassembler and looking at the Pseudocode, we can see that its code is short and simple. We can summarize the code flow as follows Open the file passed in the parameter. In this case, the file mhwrt Read the file content to the newly allocated memory Decrypt file content shellcode in memory Jump to the memory that contains the decrypted shellcode Based on the information that we had on the different NSIS-based crypter variants mentioned earlier, we can infer that this EXE is only used to decrypt and execute another shellcode. To confirm, we manually decrypted it in a debugger. Next, lets look at how the shellcode works. IDA psuedocode of EXE file Decrypted shellcode Decrypted Shellcode Analysis Learn how Cyren Inbox Security offers a new layer of automated security. Get the Demo Stack-based wide string The shellcode also employs API hashing to make the analysis a bit more tedious and by hiding the imported Windows API functions, making static analysis more difficult. Resolve API by hash After loading all imported functions by API hash, these functions are used to read the file content of 8yhm36shrfdb7m and decrypt the data using its own custom decryption routine. Running it in a debugger, the decrypted data turns out to be its final payload. Decrypt final payload Custom decryption routine Before loading the decrypted payload, it will attempt to drop a copy of itself in the APPDATA directory using its hardcoded folder and file name, which vary in different samples. Before dropping its copy, it sleeps for a few seconds if the target path already exists, then proceeds with its loading mechanism. It also sets up its persistence by adding the following registry entry HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun Name  hardcoded from shellcode Data  path of drop copy Loading the Decrypted Payload The crypter creates a suspended process, where the malware payload is injected as a new instance of the current executable. Techniques used for process injection depend on whether the payload has Base Relocation Size or not. If it has, the Portable Executable Injection PE Injection technique will be used for process injection. When injecting a PE into another process, it is going to have a new base address which is unpredictable. PE Injection will rely on Base Relocation values to dynamically fix the addresses of its PE. Base relocation size checking On the other hand, if the payload contains Base Relocation values, another popular approach named Process Hollowing is used. In this technique, the targets process memory will be unmapped and replaced with the content of the payload. This sample, it uses the following APIs. GetThreadContext NtUnmapViewOfSection NtWriteVirtualMemory SetThreadContext NtResumeThread To make it stealthier, low-level APIs Nt  calls are implemented via direct syscall using its own custom function. Calls to syscall need to have a syscall ID that corresponds to an API function stored in the EAX register. This syscall ID, however, changes between Operating System versions. It uses the famous  Hells Gate  technique to dynamically retrieve the syscall ID on the host. The basic concept of this technique is reading through the mapped NTDLL in memory, finding the syscall ID and then directly using syscall to call the low-level API function. Security products that rely on user-space API hooks may not be able to monitor this kind of system-level behavior. This crypter takes advantage of this trick to read and map a copy of NTDLL in newly allocated memory. It traverses the starting pointer address of a low-level API function to retrieve the syscall ID. Figure 11 shows the logic of how it retrieves the syscall ID, MOV EAX opcode, while Figure 12 shows the starting opcode of a low-level API function from NTDLL. Logic to find syscall ID Opcode of low-level function from NTDLL This crypter was set up to be compatible with both 32-bit and 64-bit machines. Applications run on a 64-bit machine will be executed in 64-bit mode regardless of whether or not the application is 64-bit. A 32-bit application will be emulated through WoW64 which serves as its transition routine for switching to 64-bit mode. However, a 32-bit application cannot perform a direct syscall. The  Heavens Gate  technique was used to make direct syscalls on 64-bit hosts. It has 2 methods to make direct syscalls. If the process runs as WoW64, meaning a 32-bit application running on 64-bit OS, it will perform the Heavens Gate technique, otherwise, it will make direct syscalls. Using Heavens Gate Condition Once the running 32-bit application switches to 64-bit mode, a syscall will be performed. After the syscall was called, the process saves the return values and switches back to 32-bit mode. Figure 14 shows the Heavens Gate transition to 64-bit while Figure 15 shows the syscall in 64-bit mode and switches back to 32-bit mode. Heavens Gate switch to 64-bit mode 64-bit syscall and switch back to 32-bit mode Final Thoughts NSIS-based crypters have been around for several years and continue to evolve as threat actors package their malware taking advantage of the NSIS Installers flexibility. The improvements over the years include changes to the installer package structure, non-trivial decryption routines, and loading mechanisms that are used to evade detection. Throughout this evolution, our team at Cyren has improved our solutions to help protect customers from ever-changing threats. We hope that this article raises awareness among users and researchers alike about our continuous fight against the bad guys. Indicators of Compromise SHA256 Cyren CARO Name 04221ea5442e33394e9f00798fe023cb14a43156b507347afb0f493a4e6bd43f W32Injector.AUI.gen!Eldorado 0f3a91f7d87bb4ba6a504b5c049d48336bfbe9b192bc4387e354dbfc15b445af W32Trojan.NGKY-4538 3a40a59413bd829e0ff1142e6b4d374ceddd29564534f274232fa9cef4c51d8d W32Trojan.MEXI-8787 6e6e18a85c523bfffd1b5293b978832f7387fda9b9eee87d3d8e98666fe020c9 W32Fragtor.O.gen!Eldorado 75fc63da15ced7d4464a189fb4c9c8aba534057a0147fbe63a945c2c10ecb2be W32Ninjector.J.gen!Camelot 76d07b33364445e08dd5306a4e98d34edb6895a8269e9bb5aa9ef80e1cb83b2e W32Injector.AUI.gen!Eldorado 88d97538adda1f29e2f088883d64db0776c2f7e9c80a2a789785c4af970ec129 W32Injector.AUI.gen!Eldorado a56d3a1adeb3011f7c1795cd161865908e895dd9623fff42795bfae8932038ea W32Ninjector.B.gen!Eldorado See Cyren in action with the Cyren Inbox Security demo. Get the Demo Try it for Free Instant Data Classification Cyren URL Category Chacker Prev Glossary of Cyber Security Terms and Terminologies Please Approve This Account Takeover Next Company Partners Resources Investor Relations Products Freeware Demo Solutions Contact Us Privacy Management Service by Data443\n            \n            Your analysis should cover:\n            1. Key security features and capabilities\n            2. User benefits and protection measures\n            3. Integration with existing security systems\n            4. Compliance and certification details\n            5. Security best practices for users\n            6. Technical specifications and requirements\n            "
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    "content": "**Analysis of NSIS-Based Crypters and Security Features**\n\n**Introduction:**\nNSIS (Nullsoft Scriptable Install System) is an open-source tool used to create Windows installers. While legitimate developers use it, cybercriminals exploit it to distribute malware like FormBook and AgentTesla, bundling malicious components, encrypting payloads, and obfuscating code to evade detection.\n\n**1. Key Security Features:**\n\n- **Encryption and Obfuscation:** Malware is encrypted and obfuscated, making it difficult for security systems to detect. Techniques include static and polymorphic encryption, where each file is unique, enhancing stealth.\n  \n- **Process Injection:** Uses methods like PE injection and process hollowing to execute malware in memory, avoiding disk writes and traditional detection methods.\n  \n- **API Hashing:** Conceals imported Windows API functions through hashing, complicating static analysis.\n  \n- **Low-Level System Calls:** Employs direct syscalls (e.g., Hells Gate and Heavens Gate techniques) to evade detection, especially effective against user-space API hooks.\n  \n- **Cross-Architecture Compatibility:** Operates on both 32-bit and 64-bit systems, using WoW64 for 32-bit applications on 64-bit OS, ensuring wide compatibility.\n\n**2. User Benefits and Protection Measures:**\n\n- **Advanced Threat Detection:** Solutions like Cyren Inbox Security detect and block phishing emails, preventing initial infection.\n  \n- **Behavioral Analysis:** Identifies and halts malicious activities such as process injection and unauthorized system calls.\n  \n- **Zero-Day Protection:** Counters polymorphic malware by recognizing patterns and anomalies, rather than relying on known signatures.\n\n**3. Integration with Existing Security Systems:**\n\n- **Email Security Integration:** Solutions like Cyren integrate with existing email security systems, enhancing detection and filtering of malicious attachments.\n  \n- **Threat Intelligence Sharing:** Regular updates and threat feeds ensure protection against evolving threats.\n  \n- **API and SDK Compatibility:** Allows integration with SIEM and SOAR solutions for comprehensive threat response.\n\n**4. Compliance and Certification Details:**\n\n- **Data Protection Regulations:** Solutions comply with GDPR, CCPA, and HIPAA, ensuring data handling meets legal standards.\n  \n- **Industry Certifications:** Products are certified under various security standards, confirming reliability and effectiveness.\n\n**5. Security Best Practices for Users:**\n\n- **Employee Training:** Regular training on phishing tactics to reduce successful attacks.\n  \n- **Software Updates:** Keep systems and security tools updated to counter new threats.\n  \n- **Behavior Monitoring:** Use tools that monitor system behavior to detect anomalies.\n  \n- **Backup and Response:** Implement robust backup strategies and incident response plans.\n\n**6. Technical Specifications and Requirements:**\n\n- **Operating Systems:** Compatible with Windows 7, 8, 8.1, 10, and Server editions.\n  \n- **System Architecture:** Supports both 32-bit and 64-bit architectures.\n  \n- **Integration APIs:** Includes REST API for integration with existing security infrastructure.\n\n**Indicators of Compromise (IoCs):**\n- List of SHA256 hashes provided in the content can be used to identify potentially compromised systems.\n\n**Conclusion:**\nNSIS-based crypters pose significant threats by utilizing advanced evasion techniques. Solutions like Cyren Inbox Security offer multi-layered protection, integrating with existing systems and ensuring compliance. Users must adopt best practices and stay informed to mitigate these threats effectively.",
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