Saturday, April 8, 2017

Vault7: Malware evasion and Reverse Engineering difficulty Comparison


This is basically Do's and Don'ts for a Malware author. Below table explains how a malware author can bypass different AntiVirus engines, by reversing the logic we can use similar concepts to detect the malware. Below pointers apply to PE files, Mach-O, ELF and other binaries.
EvasionRationale/Detection
DO obfuscate or encrypt all strings and configuration data that directly relate to tool functionality. Consideration should be made to also only de-obfuscating strings in-memory at the moment the data is needed. When a previously de-obfuscated value is no longer needed, it should be wiped from memory.
String data and/or configuration data is very useful to analysts and reverse-engineers.
DO NOT decrypt or de-obfuscate all string data or configuration data immediately upon execution.Raises the difficulty for automated dynamic analysis of the binary to find sensitive data.
DO explicitly remove sensitive data (encryption keys, raw collection data, shellcode, uploaded modules, etc) from memory as soon as the data is no longer needed in plain-text form.
DO NOT RELY ON THE OPERATING SYSTEM TO DO THIS UPON TERMINATION OF EXECUTION.
Raises the difficulty for incident response and forensics review.
DO utilize a deployment-time unique key for obfuscation/de-obfuscation of sensitive strings and configuration data.Raises the difficulty of analysis of multiple deployments of the same tool.
DO strip all debug symbol information, manifests(MSVC artefact), build paths, developer usernames from the final build of a binary.Raises the difficulty for analysis and reverse-engineering, and removes artefacts used for attribution/origination.
DO strip all debugging output (e.g. calls to printf(), OutputDebugString(), etc) from the final build of a tool.Raises the difficulty for analysis and reverse-engineering.
DO NOT explicitly import/call functions that is not consistent with a tool's overt functionality (i.e. WriteProcessMemory, VirtualAlloc, CreateRemoteThread, etc - for binary that is supposed to be a notepad replacement).Lowers potential scrutiny of binary and slightly raises the difficulty for static analysis and reverse-engineering.
DO NOT export sensitive function names; if having exports are required for the binary, utilize an ordinal or a benign function name.Raises the difficulty for analysis and reverse-engineering.
DO NOT generate crash dump files, core dump files, "Blue" screens, Dr Watson or other dialog pop-ups and/or other artefacts in the event of a program crash.
DO attempt to force a program crash during unit testing in order to properly verify this.
Avoids suspicion by the end user and system admins, and raises the difficulty for incident response and reverse-engineering.
DO NOT perform operations that will cause the target computer to be unresponsive to the user (e.g. CPU spikes, screen flashes, screen "freezing", etc).Avoids unwanted attention from the user or system administrator to tool's existence and behaviour.
DO make all reasonable efforts to minimize binary file size for all binaries that will be uploaded to a remote target (without the use of packers or compression). Ideal binary file sizes should be under 150KB for a fully featured tool.Shortens overall "time on air" not only to get the tool on target, but to time to execute functionality and clean-up.
DO provide a means to completely "uninstall"/"remove" implants, function hooks, injected threads, dropped files, registry keys, services, forked processes, etc whenever possible. Explicitly document (even if the documentation is  "There is no uninstall for this ") the procedures, permissions required and side effects of removal.Avoids unwanted data left on target. Also, proper documentation allows operators to make better operational risk assessment and fully understand the implications of using a tool or specific feature of a tool.
DO NOT leave dates/times such as compile timestamps, linker timestamps, build times, access times, etc. that correlate to general US core working hours (i.e. 8am-6pm Eastern time)Avoids direct correlation to origination in the United States.
DO NOT leave data in a binary file that demonstrates CIA, USG, or its witting partner companies involvement in the creation or use of the binary/tool.
Attribution of binary/tool/etc by an adversary can cause irreversible impacts to past, present and future USG operations and equities.
DO NOT have data that contains CIA and USG cover terms, compartments, operation code names  or other CIA and USG specific terminology in the binary.Attribution of binary/tool/etc by an adversary can cause irreversible impacts to past, present and future USG operations and equities.
DO NOT have "dirty words" in the binary.Dirty words, such as hacker terms, may cause unwarranted scrutiny of the binary file in question.
CIA - Central Intelligence Agency
USG - United States Government