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Community / AGENT SKILL
analyzing-position-independent-code
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Analyzes position-independent code and shellcode by identifying GetPC/PEB-walk techniques, API-hash resolution loops, and relocation-free addressing so the payload can be disassembled at the right base. Activates for requests to analyze position-independent code, identify PIC techniques, or understand how shellcode resolves APIs without imports.
Understand the trade-offs.
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Original instructions from the publisher’s SKILL.md
# Analyzing Position-Independent Code ## When to Use - You have a PIC blob/shellcode that resolves its own addresses and APIs without imports, and you need to understand its technique before disassembly. - You want to identify the base-resolution (GetPC), PEB-walk, and API-hashing mechanics. **Do not use** this to execute the code — analyze it statically (and emulate separately if needed). Treat the blob as malicious. ## Prerequisites - The PIC/shellcode blob (read inertly). ## Safety & Handling - Read bytes statically; store the blob password-protected and never execute it. ## Workflow ### Step 1: Identify PIC techniques ```bash python scripts/analyst.py analyze shellcode.bin ``` Detects GetPC stubs (`call $+5`/`fnstenv`), PEB access (`fs:[30]`/`gs:[60]`), API-hash loops (`lodsb` + `ror`), and stack-string construction. ### Step 2: Determine architecture and base behavior Confirm 32- vs 64-bit PEB access and how the code computes its own base for relative addressing. ### Step 3: Map API resolution Note the hashing algorithm and that resolved APIs are obtained by walking the PEB→LDR→export tables (pair with the API-hash resolver skill). ### Step 4: Disassemble at the right base Load the blob at the inferred base/entry in a disassembler/emulator and proceed. ## Validation - PIC technique hits reference real patterns (GetPC/PEB/API-hash), not arbitrary bytes. - Architecture is consistent with the PEB-access form detected. - The analysis points to a concrete entry/base for disassembly. ## Pitfalls - Encoded/staged shellcode where the PIC patterns appear only after decoding. - Mixed 32/64-bit (WoW64) transitions. - Custom GetPC variants not matching common signatures. ## References - See [`references/api-reference.md`](references/api-reference.md) for the analyzer. - PEB/LDR and ATT&CK T1027.007 references (linked in frontmatter).