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feat(skills): add CyberChef MCP tooling skill and documentation
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Noor Fatima
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@ -26,6 +26,13 @@ Paste the servers you want into `~/.strix/mcp-servers.json`. The example below s
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```json
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[
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{
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"name": "cyberchef",
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"transport": "stdio",
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"command": "npx",
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"args": ["-y", "cyberchef-mcp"],
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"notes": "CyberChef MCP server for multi-layer payload deobfuscation, crypto decoding, and entropy analysis."
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},
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{
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"name": "local_fs",
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"transport": "stdio",
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105
strix/skills/tooling/cyberchef.md
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105
strix/skills/tooling/cyberchef.md
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@ -0,0 +1,105 @@
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---
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name: cyberchef
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description: Multi-layer payload deobfuscation, cryptographic decoding, heuristic recipe detection (magic), and entropy analysis via CyberChef MCP.
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---
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# CyberChef MCP Tooling Playbook
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Official resources:
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- https://github.com/gchq/CyberChef
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- https://github.com/noor202401938-netizen/cyber-chef-mcp
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- https://gchq.github.io/CyberChef/
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- https://modelcontextprotocol.io
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CyberChef provides over 500 data transformation and cryptographic operations. 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 without manual intervention or guessing.
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## Canonical MCP Tool Names & Signatures
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When the `cyberchef` MCP connection is active, the following tools are available in the agent registry:
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- `cyberchef_magic(input: string)`: Run heuristic detection across known encodings, ciphers, and hash formats. Returns recommended deobfuscation recipes and confidence scores.
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- `cyberchef_bake(input: string, recipe: [{ op: string, args?: any[] }])`: Execute sequential operation chains (e.g. `[{"op": "From Base64"}, {"op": "URL Decode"}]`).
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- `cyberchef_from_base64(input: string, urlSafe?: boolean)`: Decode standard or URL-safe Base64 strings.
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- `cyberchef_to_base64(input: string, urlSafe?: boolean)`: Encode plaintext into Base64 / URL-safe Base64.
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- `cyberchef_from_hex(input: string, delimiter?: "None"|"Space"|"0x"|"Comma")`: Convert hexadecimal sequences to text.
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- `cyberchef_url_decode(input: string)`: Decode single or multi-round percent-encoded parameters.
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- `cyberchef_rot13(input: string, amount?: number)`: Rotate characters by offset (default 13, Caesar cipher support).
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- `cyberchef_xor(input: string, key: string, keyFormat?: "UTF8"|"Hex")`: Decrypt or apply bitwise XOR with secret key.
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- `cyberchef_jwt_decode(token: string)`: Parse and inspect header, claims, alg, and signatures of JSON Web Tokens.
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- `cyberchef_entropy(input: string)`: Calculate Shannon entropy (0.0 to 8.0) to distinguish plaintext, compressed data, and encrypted or packed payloads.
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- `cyberchef_defang_url(url: string)`: Defang malicious or suspicious indicators (`hxxps://target[.]com`) for safe reporting.
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- `cyberchef_extract_entities(text: string)`: Extract URLs, IP addresses, and email addresses from raw logs or memory strings.
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## Agent-Safe Baseline for Automation
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1. **Heuristic First**:
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Always run `cyberchef_magic` on unknown high-entropy or encoded strings before guessing transformations:
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```json
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{
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"tool": "cyberchef_magic",
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"arguments": { "input": "ZXlKaGJHY2lPaUpTVXpVbkxh..." }
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}
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```
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2. **Sequential Multi-Layer Deobfuscation (Bake)**:
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For payloads with layered obfuscation (e.g. Hex inside Base64 inside URL-encoded query params):
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```json
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{
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"tool": "cyberchef_bake",
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"arguments": {
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"input": "%34%38%36%35%36%63%36%63%36%66",
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"recipe": [
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{ "op": "URL Decode" },
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{ "op": "From Hex", "args": ["None"] }
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]
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}
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}
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```
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3. **High-Entropy Verification**:
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Before analyzing suspicious parameters, assess randomness and encryption depth:
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```json
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{
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"tool": "cyberchef_entropy",
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"arguments": { "input": "01a2fe89cb994821a0d8e4..." }
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}
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```
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- **Entropy < 4.0**: Plain English text, uncompressed source code, or structured JSON/XML.
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- **Entropy 4.0 - 6.5**: Encoded payloads (Base64, Hex) or compressed data.
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- **Entropy > 7.0**: Strong encryption, cryptographic hashes, or packed binary shellcode.
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## Common Security Analysis Patterns
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### Pattern 1: Nested WAF Bypass / Obfuscated Injection Vector
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When target web applications accept encoded input in parameters or cookies:
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1. Extract candidate parameter from HTTP request or response.
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2. Call `cyberchef_magic` to determine layers.
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3. Call `cyberchef_bake` with the suggested pipeline to recover the plaintext injection string.
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4. Verify whether the underlying query contains unsanitized SQLi (`UNION SELECT`), XSS, or SSRF vectors.
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### Pattern 2: JWT Security Inspection
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When encountering `Authorization: Bearer <token>` or session tokens:
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1. Call `cyberchef_jwt_decode(token)`.
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2. Inspect the header: check for `alg: "none"`, `alg: "HS256"` with potential asymmetric public key confusion, or empty signatures.
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3. Inspect claims: verify expiry timestamps (`exp`), issuer (`iss`), role/privilege elevations, and user identities.
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### Pattern 3: XOR Obfuscation Recovery
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When inspecting hardcoded binary strings, PowerShell scripts, or obfuscated malware droppers:
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1. Identify probable key length or common plaintext prefix (e.g., `MZ`, `http`, `function`).
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2. Run `cyberchef_xor` iterating candidate keys to extract underlying C2 endpoints or script payloads.
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## Critical Correctness Rules
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- **Do Not Guess Encodings**: If a string contains `=, %, 0x` or unexpected symbols, run `cyberchef_magic` first rather than blindly applying base64 or URL decoding.
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- **Preserve Raw Inputs**: Keep the original obfuscated string in agent memory/notes alongside the decoded output for accurate proof-of-concept (PoC) reporting.
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- **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.
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- **Safe Defanging**: Always run `cyberchef_defang_url` on confirmed malicious or C2 URLs before writing final markdown reports.
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## Failure Recovery
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- If `cyberchef_from_base64` throws a padding error, retry with `urlSafe: true` or inspect whether characters are URL percent-encoded first.
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- If `cyberchef_from_hex` produces unprintable garbage characters, check if the input is big-endian or uses custom delimiters (`0x`, `Space`, `,`).
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- If `cyberchef_bake` returns an error, use `cyberchef_help(query: "<operation>")` to verify supported operation names and argument formats.
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If uncertain, query web_search with:
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`site:gchq.github.io/CyberChef cyberchef <operation_name>`
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