From 1fb92788db94aa6a9c20cb827ee0ccea4e82037a Mon Sep 17 00:00:00 2001 From: Noor Fatima Date: Tue, 29 Sep 2026 21:18:53 +0500 Subject: [PATCH] fix(skills): add raw-byte entropy workflow and in-engine bake chaining --- strix/skills/tooling/cyberchef.md | 68 +++++++++++++++++++++++++++---- 1 file changed, 60 insertions(+), 8 deletions(-) diff --git a/strix/skills/tooling/cyberchef.md b/strix/skills/tooling/cyberchef.md index e2bc0c15..d618a161 100644 --- a/strix/skills/tooling/cyberchef.md +++ b/strix/skills/tooling/cyberchef.md @@ -11,7 +11,7 @@ Official resources: - https://gchq.github.io/CyberChef/ - https://modelcontextprotocol.io -CyberChef MCP provides 28 core data transformation, cryptographic, and forensic operations with zero external dependencies. Connected via the Model Context Protocol (MCP) server `cyberchef`, it enables Strix agents to autonomously analyze, deobfuscate, unpack, and verify encoded exploit payloads, authorization tokens, and obfuscated attack vectors with deterministic sub-millisecond execution. +CyberChef MCP provides 33 core data transformation, cryptographic, compression (Gunzip, Gzip, Zlib, Raw Deflate), and forensic operations with zero external dependencies. Connected via the Model Context Protocol (MCP) server `cyberchef`, it enables Strix agents to autonomously analyze, deobfuscate, unpack, and verify encoded exploit payloads, authorization tokens, and obfuscated attack vectors with deterministic sub-millisecond execution. ## MCP Discovery & Dispatch Workflow @@ -74,8 +74,13 @@ For payloads with layered obfuscation (e.g. Hex inside Base64 inside URL-encoded } ``` -### 3. Entropy Assessment & Encoding Representation Calibration -When evaluating whether a payload or parameter is encrypted, packed shellcode, or benign text, evaluate Shannon entropy through `call_mcp`: +### 3. Entropy Assessment & Raw-Byte Workflow +When evaluating whether a payload or parameter is encrypted, packed shellcode, or benign text, evaluate Shannon entropy through `call_mcp`. + +Depending on whether you are assessing an encoded representation directly or require true 8-bit raw-byte entropy, use one of the two workflows below: + +#### Workflow A: Direct Representation-Calibrated Entropy (`cyberchef_entropy`) +Pass the encoded string (Hex or Base64) directly to `cyberchef_entropy` without prior decoding: ```json { "tool": "call_mcp", @@ -88,6 +93,7 @@ When evaluating whether a payload or parameter is encrypted, packed shellcode, o } } ``` +`cyberchef_entropy` automatically detects the representation alphabet and returns `shannonEntropy`, `bitsPerChar`, `maxForAlphabet`, and `normalizedRatio` (saturation). > [!IMPORTANT] > **Calibrate entropy thresholds by input encoding representation:** @@ -99,11 +105,51 @@ When evaluating whether a payload or parameter is encrypted, packed shellcode, o > - **Base64 Strings (64 characters, max 6.0 bits/char)**: > - *Plain text Base64*: ~3.8 – 4.5 > - *High-entropy ciphertext / packed data*: **5.7 – 6.0** (Cannot exceed 6.0!) -> - **Raw Binary / Decoded Byte Streams (256 values, max 8.0 bits/byte)**: -> - *Plain text / uncompressed source code*: < 4.5 -> - *Compressed archives / packed code / encrypted shellcode*: > 7.2 -> -> **Best Practice**: Decode encoded representations (Hex, Base64) to raw bytes via `cyberchef_from_hex` or `cyberchef_from_base64` before evaluating raw Shannon entropy. +> - **Normalized Saturation Rule**: If `normalizedRatio >= 0.85` (or `verdict == "encrypted_or_compressed"`), the payload is near-maximal entropy for its alphabet, indicating encryption, CSPRNG keys, or compressed data. + +#### Workflow B: Atomic Raw-Byte Entropy via `cyberchef_bake` (Recommended for Raw Binary Streams) +To evaluate true 8-bit Shannon entropy (max 8.0 bits/byte) on an encoded payload (Base64 or Hex), execute the decode operation and entropy analysis **atomically** in a single `cyberchef_bake` recipe: +```json +{ + "tool": "call_mcp", + "arguments": { + "connection": "cyberchef", + "tool": "cyberchef_bake", + "arguments": { + "input": "rLYFVVXj/6ydut5XjZodQFTcIX3qdGy5lS4CBmdY...", + "recipe": [ + { "op": "From Base64" }, + { "op": "Entropy" } + ] + } + } +} +``` +For Hex-encoded payloads: +```json +{ + "tool": "call_mcp", + "arguments": { + "connection": "cyberchef", + "tool": "cyberchef_bake", + "arguments": { + "input": "4a8f1b9c2d3e4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b...", + "recipe": [ + { "op": "From Hex", "args": ["None"] }, + { "op": "Entropy" } + ] + } + } +} +``` +This in-engine pipeline keeps raw decoded byte buffers in memory without serializing non-UTF-8 bytes across the JSON-RPC boundary. The returned entropy report uses the 8-bit raw alphabet (`maxForAlphabet: 8`): +- **Raw Binary / Decoded Byte Streams (256 values, max 8.0 bits/byte)**: + - *Plain text / uncompressed source code*: < 4.5 bits/byte + - *Compressed archives / packed code / encrypted shellcode*: > 7.2 bits/byte + +> [!CAUTION] +> **Do NOT attempt multi-turn raw byte passing across `call_mcp`:** +> `call_mcp` transports inputs and outputs over JSON-RPC strings. Arbitrary 8-bit binary bytes (such as non-printable ciphertext or compressed streams) cannot be safely represented or transported across JSON-RPC without corruption (mojibake, Unicode replacement characters `\uFFFD`, or truncation). Never call `cyberchef_from_base64` or `cyberchef_from_hex` and then attempt to pass the resulting string to `cyberchef_entropy` in a second `call_mcp` call. Always use `cyberchef_bake` to chain decoding and entropy atomically, or evaluate representation-calibrated entropy directly on the encoded string via `cyberchef_entropy`. ## Common Security Analysis Patterns @@ -125,9 +171,15 @@ When inspecting hardcoded binary strings, PowerShell scripts, or obfuscated malw 1. Identify probable key length or common plaintext prefix (e.g., `MZ`, `http`, `function`). 2. Run `call_mcp(connection="cyberchef", tool="cyberchef_xor", arguments={"input": data, "key": candidate_key})` iterating candidate keys to extract underlying C2 endpoints or script payloads. +### Pattern 4: Encrypted / Compressed Payload & Entropy Classification +When verifying whether an unknown string parameter is ciphertext, packed shellcode, or a high-entropy secret token: +1. **Calibrated check**: Call `call_mcp(connection="cyberchef", tool="cyberchef_entropy", arguments={"input": candidate})`. Inspect `normalizedRatio` and `verdict`. If `normalizedRatio >= 0.85`, it is probable ciphertext or compressed data. +2. **Raw-byte verification**: If strict 8-bit thresholds (> 7.2 bits/byte) are required, run `call_mcp(connection="cyberchef", tool="cyberchef_bake", arguments={"input": candidate, "recipe": [{"op": "From Base64"}, {"op": "Entropy"}]})` (or `From Hex`). + ## Critical Correctness Rules - **Use `call_mcp` Dispatch**: Never attempt to call CyberChef tools directly as top-level agent tools. Always dispatch through `call_mcp(connection="cyberchef", tool="...", arguments={...})`. +- **Atomic Raw-Byte Entropy Execution**: Never attempt to pass decoded raw binary bytes between separate `call_mcp` calls. JSON-RPC cannot transport arbitrary non-printable bytes without corruption. When evaluating raw byte entropy for Base64 or Hex payloads, always chain `From Base64`/`From Hex` and `Entropy` atomically in a single `cyberchef_bake` recipe. - **Do Not Guess Encodings**: If a string contains `=, %, 0x` or unexpected symbols, run `cyberchef_magic` first rather than blindly applying base64 or URL decoding. - **Preserve Raw Inputs**: Keep the original obfuscated string in agent memory/notes alongside the decoded output for accurate proof-of-concept (PoC) reporting. - **Fail-Safe Fallback**: If an operation fails during `cyberchef_bake`, isolate the failing recipe step and execute individual tools (`cyberchef_from_base64`, `cyberchef_url_decode`) sequentially via `call_mcp`.