mandiant/capa-rules

rule idea: zlib fast inflate

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#494 opened on Nov 4, 2021

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good first issuerule idea

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Description

see source: https://github.com/madler/zlib/blob/master/contrib/masmx86/inffas32.asm

I've seen this code used in shellcode; we can hit on the hard-coded strings or the assembly itself.

strings:

  • Fast decoding Code from Chris Anderson
  • invalid literal/length code
  • invalid distance code
  • invalid distance too far back

Contributor guide

Research direction
Study existing capa rules for similar patterns, then create a rule that matches the provided strings or the assembly instructions. Use capa's rule testing to validate.
Tech stack
python
Domain
securitytooling
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
Assemblycapa rules syntax
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
55