Check Point Research demonstrated that cloud-based static analysis with ChatGPT (using exported IDA data) combined with occasional MCP-assisted runtime checks can drastically accelerate reverse engineering of heavily obfuscated XLoader 8.0, enabling rapid recovery of keys, decrypted functions, strings, and C2 domains. The workflow reduced many manual steps (triage, deobfuscation, scripting, validation) from days to hours while still requiring targeted human adjustments for scattered key derivation and sample-specific quirks. #XLoader #RC4 #ChatGPT
Keypoints
- XLoader 8.0 uses multiple layered protections (on-the-fly function decryption, custom RC4 variants, obfuscated API resolution, secure-call trampolines, and C2 camouflage) that make static and dynamic analysis difficult.
- CPR built an “offline” pipeline exporting IDA data (functions.jsonl, decomp/*.c, strings.jsonl, sample.bin) and used ChatGPT to perform deep static analysis, generate scripts, and run tests inside the ChatGPT environment.
- Generative AI (GPT‑5) identified cryptographic routines, reproduced modified RC4 algorithms, and produced working decryptor scripts and IDAPython tools much faster than manual development; some tasks still required MCP-driven runtime checks to capture keys.
- Three distinct function-decryption schemes were discovered in XLoader (6-byte markers + per-function XOR modifier; 4-byte markers + two-layer decryption with marker-derived key; wrapper-embedded 20-byte keys with modifiers), requiring iterative decryptors to recover 101 functions.
- AI-assisted API-hash deobfuscation and string decryption scripts allowed recovery of 175 strings and automated annotation of resolved Module!Function names, including detection of sandbox-evasion hashes.
- Domain extraction required peeling multiple layers (Base64 + at least two modified-RC4 layers); some keys (ctx+0x23D0, SALT_DWORD) had to be located manually or via MCP to successfully decrypt domain names.
- The combined approach (offline ChatGPT static analysis + selective MCP debugging) reduced turnaround time from days to hours but still depends on human verification and ad-hoc fixes for robust, generic tooling.
MITRE Techniques
- [T1055 ] Process Injection – XLoader performs injections into system processes to hide execution and evade analysis, described as “injections into system processes” in the sample overview.
- [T1027 ] Obfuscated Files or Information – The malware uses multiple layers of encryption and obfuscated API calls: “…customized encryption with additional mixing steps, encrypted blocks disguised as valid but meaningless assembly code, obfuscated API calls…”
- [T1218 ] Signed Binary Proxy Execution (abuse) – Secure-call trampoline temporarily encrypts most of the image before invoking function pointers to hide calls and thwart hooking: “…it temporarily encrypts nearly the entire image before invoking a function pointer and then decrypts those same regions once the call returns.”
- [T1497 ] Virtualization/Sandbox Evasion – Aggressive evasion checks and sandbox-detection logic prevent malicious branches from running: “XLoader checks for signs of virtual machines and analysis tools. If it detects them, the malicious branch may never run at all.”
- [T1003 ] Credential Dumping (data exfiltration payload behavior) – XLoader is an information stealer (loader) that collects data and communicates with C2 infrastructure: “XLoader is a widely observed malicious loader with information-stealing capabilities.”
- [T1041 ] Exfiltration Over C2 Channel – Encrypted network traffic and real C2 addresses hidden among many decoys used for command-and-control: “XLoader encrypts its network traffic, and hides real C2 addresses among dozens of decoys and fake domains.”
- [T1609 ] Software Packing – The sample contains a built-in packer and on-the-fly decryption routines that unpack code at runtime: “Version 5 introduced a built-in packer…cases where multi-layer encryption is applied…on-the-fly function decryption.”
Indicators of Compromise
- [SHA256 ] sample identifier – SHA256 77db3fdccda60b00dd6610656f7fc001948cdcf410efe8d571df91dd84ae53e1 (XLoader 8.0 sample)
- [File name / binary ] sample context – sample.bin exported from IDA export bundle (used for offline decryption and script execution)
- [Domain ] decrypted C2 candidates – examples include taxi-in[.]online, taskcomputer[.]xyz, synergydrop[.]xyz (first 3 of 64 decrypted domains)
- [Function EA ] code context – notable function addresses used in analysis: oep_start 0x00430CB3, ai_dec_func_0 0x00404913, ai_dec_func_11 0x004095F3 (used to derive keys), and ai_dec_func_20 0x00411053 (SALT_DWORD init)
- [Script / artifact ] tooling outputs – suggestions.json (function rename/comments), and decrypted strings list (175 decrypted strings) used as analysis artifacts
Read more: https://research.checkpoint.com/2025/generative-ai-for-reverse-engineering/