CIA: How Malware Should Be Written To Avoid Fingerprints
Development Tradecraft DOs and DON’Ts
SECRET//NOFORN
(U) General (e.g. all PE/Mach-O/ELF or other binary files)
| Directive | Rationale |
|---|---|
| (S//NF) 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. | (S//NF) String data and/or configuration data is very useful to analysts and reverse-engineers. |
| (S//NF) DO NOT decrypt or de-obfuscate all string data or configuration data immediately upon execution. | (S//NF) Raises the difficulty for automated dynamic analysis of the binary to find sensitive data. |
| (S//NF) 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. | (S//NF) Raises the difficulty for incident response and forensics review. |
| (S//NF) DO utilize a deployment-time unique key for obfuscation/de-obfuscation of sensitive strings and configuration data. | (S//NF) Raises the difficulty of analysis of multiple deployments of the same tool. |
| (S//NF) DO strip all debug symbol information, manifests(MSVC artifact), build paths, developer usernames from the final build of a binary. | (S//NF) Raises the difficulty for analysis and reverse-engineering, and removes artifacts used for attribution/origination. |
| (U//FOUO) DO strip all debugging output (e.g. calls to printf(), OutputDebugString(), etc) from the final build of a tool. | (S//NF) Raises the difficulty for analysis and reverse-engineering. |
| (S//NF) 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). | (S//NF) Lowers potential scrutiny of binary and slightly raises the difficulty for static analysis and reverse-engineering. |
| (S//NF) DO NOT export sensitive function names; if having exports are required for the binary, utilize an ordinal or a benign function name. | (S//NF) Raises the difficulty for analysis and reverse-engineering. |
| (S//NF) DO NOT generate crashdump files, coredump files, “Blue” screens, Dr Watson or other dialog pop-ups and/or other artifacts in the event of a program crash. DO attempt to force a program crash during unit testing in order to properly verify this. | (S//NF) Avoids suspicion by the end user and system admins, and raises the difficulty for incident response and reverse-engineering. |
| (S//NF) 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). | (S//NF) Avoids unwanted attention from the user or system administrator to tool’s existence and behavior. |
| (S//NF) 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. | (S//NF) Shortens overall “time on air” not only to get the tool on target, but to time to execute functionality and clean-up. |
| (S//NF) 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 <feature>”) the procedures, permissions required and side effects of removal. | (S//NF) 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. |
| (S//NF) 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) | (S//NF) Avoids direct correlation to origination in the United States. |
| (S//NF) 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. | (S//NF) Attribution of binary/tool/etc by an adversary can cause irreversible impacts to past, present and future USG operations and equities. |
| (S//NF) 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. | (S//NF) Attribution of binary/tool/etc by an adversary can cause irreversible impacts to past, present and future USG operations and equities. |
| (S//NF) DO NOT have “dirty words” (see dirty word list – TBD) in the binary. | (S//NF) Dirty words, such as hacker terms, may cause unwarranted scrutiny of the binary file in question. |
(U) Networking
| Directive | Rationale |
|---|---|
| (U//FOUO) DO use end-to-end encryption for all network communications. NEVER use networking protocols which break the end-to-end principle with respect to encryption of payloads. | (S//NF) Stifles network traffic analysis and avoids exposing operational/collection data. |
| (S//NF) DO NOT solely rely on SSL/TLS to secure data in transit. | (S//NF) Numerous man-in-middle attack vectors and publicly disclosed flaws in the protocol. |
| (S//NF) DO NOT allow network traffic, such as C2 packets, to be re-playable. | (S//NF) Protects the integrity of operational equities. |
| (S//NF) DO use ITEF RFC compliant network protocols as a blending layer. The actual data, which must be encrypted in transit across the network, should be tunneled through a well known and standardized protocol (e.g. HTTPS) | (S//NF) Custom protocols can stand-out to network analysts and IDS filters. |
| (S//NF) DO NOT break compliance of an RFC protocol that is being used as a blending layer. (i.e. Wireshark should not flag the traffic as being broken or mangled) | (S//NF) Broken network protocols can easily stand-out in IDS filters and network analysis.
|
| (S//NF) DO use variable size and timing (aka jitter) of beacons/network communications. DO NOT predicatively send packets with a fixed size and timing. | (S//NF) Raises the difficulty of network analysis and correlation of network activity. |
| (S//NF) DO proper cleanup of network connections. DO NOT leave around stale network connections. | (S//NF) Raises the difficulty of network analysis and incident response. |
(U)Disk I/O
| Directive | Rationale |
|---|---|
| (S//NF) DO explicitly document the “disk forensic footprint” that could be potentially created by various features of a binary/tool on a remote target. | (S//NF) Enables better operational risk assessments with knowledge of potential file system forensic artifacts. |
| (S//NF) DO NOT read, write and/or cache data to disk unnecessarily. Be cognizant of 3rd party code that may implicitly write/cache data to disk. | (S//NF) Lowers potential for forensic artifacts and potential signatures. |
| (S//NF) DO NOT write plain-text collection data to disk. | (S//NF) Raises difficulty of incident response and forensic analysis. |
| (S//NF) DO encrypt all data written to disk. | (S//NF) Disguises intent of file (collection, sensitive code, etc) and raises difficulty of forensic analysis and incident response. |
| (S//NF) DO utilize a secure erase when removing a file from disk that wipes at a minimum the file’s filename, datetime stamps (create, modify and access) and its content. (Note: The definition of “secure erase” varies from filesystem to filesystem, but at least a single pass of zeros of the data should be performed. The emphasis here is on removing all filesystem artifacts that could be useful during forensic analysis) | (S//NF) Raises difficulty of incident response and forensic analysis. |
| (S//NF) DO NOT perform Disk I/O operations that will cause the system to become unresponsive to the user or alerting to a System Administrator. | (S//NF) Avoids unwanted attention from the user or system administrator to tool’s existence and behavior. |
| (S//NF) DO NOT use a “magic header/footer” for encrypted files written to disk. All encrypted files should be completely opaque data files. | (S//NF) Avoids signature of custom file format’s magic values. |
| (S//NF) DO NOT use hard-coded filenames or filepaths when writing files to disk. This must be configurable at deployment time by the operator. | (S//NF) Allows operator to choose the proper filename that fits with in the operational target. |
| (S//NF) DO have a configurable maximum size limit and/or output file count for writing encrypted output files. | (S//NF) Avoids situations where a collection task can get out of control and fills the target’s disk; which will draw unwanted attention to the tool and/or the operation. |
(U) Dates/Time
| Directive | Rationale |
|---|---|
| (U//FOUO) DO use GMT/UTC/Zulu as the time zone when comparing date/time. | (S//NF) Provides consistent behavior and helps ensure “triggers/beacons/etc” fire when expected. |
| (S//NF) DO NOT use US-centric timestamp formats such as MM-DD-YYYY. YYYYMMDD is generally preferred. | (S//NF) Maintains consistency across tools, and avoids associations with the United States. |
(S//NF) PSP/AV
| Directive | Rationale |
|---|---|
| (S//NF) DO NOT assume a “free” PSP product is the same as a “retail” copy. Test on all SKUs where possible. | (S//NF) While the PSP/AV product may come from the same vendor and appear to have the same features despite having different SKUs, they are not. Test on all SKUs where possible. |
| (S//NF) DO test PSPs with live (or recently live) internet connection where possible. NOTE: This can be a risk vs gain balance that requires careful consideration and should not be haphazardly done with in-development software. It is well known that PSP/AV products with a live internet connection can and do upload samples software based varying criteria. | (S//NF) PSP/AV products exhibit significant differences in behavior and detection when connected to the internet vise not. |
(S//NF) Encryption
(S//NF) NOD publishes a Cryptography standard: “NOD Cryptographic Requirements v1.1 TOP SECRET.pdf“. Besides the guidance provided here, the requirements in that document should also be met.
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