analyzing-dotnet-malware-internals

analyzing-dotnet-malware-internals is a skill for Claude Code, Codex from meltedinhex/analyst-ai-pack. It costs 72 tokens per session (792 once invoked), scanned A, original, Apache-2.0.

A static-analysis guide for .NET malware, malicious software built for Microsoft's managed runtime. It converts its intermediate code into readable C# and follows loaders that bring another payload into memory.

In plain words
What is it for?
Use it to confirm that a sample is a .NET assembly, decompile it, recover encrypted strings, inspect startup code, and trace reflection-based payload loading.
Why use it?
It helps analysts understand code hidden by .NET obfuscation, such as encrypted strings or confusing control flow. It avoids using native-code tools as the main approach for managed programs.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to confirm that a sample is a .NET assembly, decompile it, recover encrypted strings, inspect startup code, and trace reflection-based payload loading.

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Install with agentmods
npx agentmods add skills/meltedinhex/analyst-ai-pack/analyzing-dotnet-malware-internals
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add meltedinhex/analyst-ai-pack --skill analyzing-dotnet-malware-internals
Clone the repo
git clone --depth 1 https://github.com/meltedinhex/analyst-ai-pack

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for analyzing-dotnet-malware-internals

README.md
[![agentmods](https://agentmods.dev/badge/skills/meltedinhex/analyst-ai-pack/analyzing-dotnet-malware-internals/github.svg)](https://agentmods.dev/skills/meltedinhex/analyst-ai-pack/analyzing-dotnet-malware-internals)
Your own site
<a href="https://agentmods.dev/skills/meltedinhex/analyst-ai-pack/analyzing-dotnet-malware-internals"><img src="https://agentmods.dev/badge/skills/meltedinhex/analyst-ai-pack/analyzing-dotnet-malware-internals/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for analyzing-dotnet-malware-internals

Your own site · 80×15
<a href="https://agentmods.dev/skills/meltedinhex/analyst-ai-pack/analyzing-dotnet-malware-internals"><img src="https://agentmods.dev/badge/skills/meltedinhex/analyst-ai-pack/analyzing-dotnet-malware-internals.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 72 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 792 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00072 $0.00792
Opus 5 $0.00036 $0.00396
Sonnet 5 $0.00014 $0.00158
Haiku 4.5 $0.00007 $0.00079

Measured 9d ago against content hash 1f743167cb69, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

analyzing-dotnet-malware-internals scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/analyst.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/analyzing-dotnet-malware-internals/SKILL.md · 97 lines

How it starts

The opening of the file, as written. The whole thing — 97 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Analyzing .NET Malware Internals

When to Use

  • A sample is a managed (.NET) assembly — confirmed by a CLR header / mscoree import or BSJB metadata signature.
  • You need readable C# from MSIL and want to defeat .NET-specific obfuscation.
  • A loader uses reflection (Assembly.Load) to run an in-memory payload you must recover.

Do not use native disassembly workflows (Ghidra for x86) as the primary tool — managed code decompiles far more cleanly with a .NET decompiler.

Prerequisites

  • ILSpy / dnSpyEx for decompilation and (with dnSpyEx) managed debugging.
  • de4dot or equivalent for known protectors; familiarity with common .NET obfuscators.

Workflow

Step 1: Confirm it is managed

Check for the CLR runtime header and the BSJB metadata magic:

python scripts/analyst.py identify sample.exe

Step 2: Decompile

Open in ILSpy/dnSpyEx and review the entry point, Main, and module initializer (<Module>.cctor), which protectors often abuse.

Step 3: Handle obfuscation

Recognize and undo common schemes:

  • String encryption — a decryptor method called everywhere; run/trace it to recover plaintext (de4dot can often static-decrypt).
  • Control-flow flattening — follow the dispatcher state machine.
  • Proxy methods / renaming — rely on decompiler analysis rather than names.

Step 4: Trace reflection loaders

Find Assembly.Load(byte[]) / Activator.CreateInstance; dump the byte array argument at runtime (managed debugger breakpoint) to recover the real second-stage assembly, then recurse.

Step 5: Analyze the payload

Decompile the recovered stage; extract C2, configuration, and capabilities for the report.

Validation

  • Decompiled C# is coherent (named or recovered) and the entry path is traced.
  • Encrypted strings are recovered to plaintext.
  • The reflection-loaded stage is dumped and itself decompiles.

Pitfalls

  • Treating the loader as the payload — managed malware is frequently multi-stage.
  • Ignoring the module initializer where protectors install hooks.
  • Static-decrypting strings when the scheme is runtime-keyed; debug and dump instead.

Read the full file on GitHub · 97 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 9d ago First seen · 97 lines · 72 tokens per session scan A 1f743167cb69

Subscribe to this mod's changes

analyzing-dotnet-malware-internals is a skill published in the GitHub repository meltedinhex/analyst-ai-pack (22 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 72 tokens to every session and 792 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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