SecureZip

Table of contents

• Description and general info
  • Installation
  • Usage
  • Example output

Description / General info

I couldn't find an opensource ZipBomb blocker, so this is my attempt at making one.

It is a work in progress, but the scan feature is usable and safe_extract works for linux.

DO NOT EXTRACT THE EXAMPLE ZIPS! It will make you sad. No one wants you to be sad.

They are malicious by intent and only for testing purposes.

Installation:

pip install SecureZip

Usage:

SecureZip.Loader parameters:

• [REQUIRED] zip_file: Path to zip
• [OPTIONAL] ratio_threshold: compression ratio threshold when to rule the zip malicious. Default = 1032
• [OPTIONAL] nested_zips_limit: Total zip count when to abort and rule the zip malicious. Default = 3
• [OPTIONAL] nested_levels_limit: Limit when to abort travelling the zips and rule the zip malicious. Default = 2
• [OPTIONAL] killswitch_seconds: Seconds to allow traversing the zip. After the limit is hit, zip is ruled malicious. Default = 1
• [OPTIONAL] symlinks_allowed: Boolean. Default = False
• [OPTIONAL] directory_travelsal_allowed: Boolean. Default = False

Loader methods:

• is_dangerous() -> bool
• has_travelsal() -> bool
• has_links() -> bool

from pathlib import Path
import SecureZip

file = Path('myzip.zip')
zip = SecureZip.Loader(zip_file=file)
if zip.scan() and zip.get_compression_ratio() > 1032:
    print(zip.output())
else:
    #do something with the zip

from pathlib import Path
import SecureZip

file = Path('myzip.zip')
zip = SecureZip.Loader(zip_file=file)
zip.scan() # Returns true when zip should be considered malicious
if zip.is_dangerous(): # Returns true when zip should be considered malicious
    do stuff

Example output from output() after calling scan() -> bool

• Single file in zip

    Dangerous: False
    Message = Success
    Compression Ratio = 0.77 Uncompressed size: 907.00 bytes Compressed size: 1.16 kilobytes
    Nested zips = 0
    Nest Levels = 0
    Symlinks = False
  

• Double nested zips -- with maximum nesting set to 4 : SecureZip.Loader(..., nested_zips_limit=4)

    Dangerous: True
    Message = Success
    Compression Ratio = 0.58 Uncompressed size: 922.00 bytes Compressed size: 1.55 kilobytes
    Nested zips = 5
    Nest Levels = 2
    Symlinks = False
  

• 97tb / 14,5kb zipbomb -- with 5s killswitch enabled to prevent long scan time : SecureZip.Loader(..., killswitch_seconds=5)

    Dangerous: True
    Message = Killswitch enabled due to too deep recursion or timeout, values collected are valid only to that point
    Compression Ratio = 125869951.52 Uncompressed size: 1.69 terabytes Compressed size: 14.45 kilobytes
    Nested zips = 1930
    Nest Levels = 100
    Symlinks = False
  

• 4.5pb / 46mb BAMSOFTWARE zbxl FLAT zipbomb

    Dangerous: True
    Message = Success
    Compression Ratio = 98262444.02 Uncompressed size: 4.00 petabytes Compressed size: 43.75 megabytes
    Nested zips = 0
    Nest Levels = 0
    Symlinks = False