safezip 0.1.6

Hardened ZIP extraction for Python - secure by default.

Hardened ZIP extraction for Python - secure by default.

safezip is a zero-dependency, production-grade wrapper around Python’s zipfile module that defends against the most common ZIP-based attacks: ZipSlip path traversal, ZIP bombs, and malformed/crafted archives.

Features

• ZipSlip protection - relative traversal, absolute paths, Windows UNC paths, Unicode lookalike attacks, and null bytes in filenames are all blocked.

• ZIP bomb protection - per-member and cumulative decompression ratio limits abort extraction before runaway decompression can exhaust disk or memory.

• File size limits - per-member size is checked against the declared header value at open time (Guard phase) and again against actual decompressed bytes during streaming (Streamer phase). Total extraction size is enforced cumulatively across all members at stream time.

• ZIP64 consistency checks - crafted archives with inconsistent ZIP64 extra fields are rejected before decompression begins.

• Symlink policy - configurable: REJECT (default), IGNORE, or RESOLVE_INTERNAL (symlink entries are extracted as regular files; no OS symlink is created on disk).

• Atomic writes - every member is written to a temporary file first; the destination is only created after all checks pass. No partial files are left on disk after a security abort.

• Secure by default - all limits are active without any configuration.

• Zero dependencies - standard library only.

• Environment variable overrides - all limits (including symlink_policy) can be set via SAFEZIP_* environment variables for containerised deployments.

Prerequisites

Python 3.10 or later. No additional packages required.

Installation

With uv:

uv pip install safezip

Or with pip:

pip install safezip

Quick start

Drop-in replacement for the common zipfile extraction pattern:

from safezip import safe_extract

safe_extract("path/to/file.zip", "/var/files/extracted/")

Or use the SafeZipFile context manager for more control:

from safezip import SafeZipFile

with SafeZipFile("path/to/file.zip") as zf:
    print(zf.namelist())
    zf.extractall("/var/files/extracted/")

Custom limits

See the Default limits for reference.

from safezip import SafeZipFile, SymlinkPolicy

with SafeZipFile(
    "path/to/file.zip",
    max_file_size=100 * 1024 * 1024,      # 100 MiB per member (default: 1 GiB)
    max_total_size=500 * 1024 * 1024,     # 500 MiB total (default: 5 GiB)
    max_files=1_000,                      # (default: 10 000)
    max_per_member_ratio=50.0,            # (default: 200)
    max_total_ratio=50.0,                 # (default: 200)
    max_nesting_depth=1,                  # (default: 3)
    symlink_policy=SymlinkPolicy.IGNORE,  # (default: SymlinkPolicy.REJECT)
) as zf:
    zf.extractall("/var/files/extracted/")

Recursive extraction

When an archive contains nested .zip files, set recursive=True to descend into them automatically. All safety limits apply at every level. Each nested archive is extracted into a directory named after it (without the extension). The .zip file itself is never written to disk.

from safezip import SafeZipFile

# archive.zip
#   readme.txt
#   data.zip          ← will be descended into, not extracted as a blob
#     report.csv

with SafeZipFile("path/to/archive.zip", recursive=True, max_nesting_depth=3) as zf:
    zf.extractall("/var/files/extracted/")

# Result on disk:
#   /var/files/extracted/readme.txt
#   /var/files/extracted/data/report.csv

With max_nesting_depth=0, opening any nested archive raises NestingDepthError before extracting a single byte from it:

import pytest
from safezip import SafeZipFile, NestingDepthError

# archive.zip
#   readme.txt
#   data.zip          ← depth 1 exceeds max_nesting_depth=0 → NestingDepthError
#     report.csv

with pytest.raises(NestingDepthError):
    with SafeZipFile(
        "path/to/archive.zip", recursive=True, max_nesting_depth=0
    ) as zf:
        zf.extractall("/var/files/extracted/")

Security event monitoring

from safezip import SafeZipFile, SecurityEvent

def my_monitor(event: SecurityEvent) -> None:
    print(f"[safezip] {event.event_type} archive={event.archive_hash}")

with SafeZipFile("path/to/file.zip", on_security_event=my_monitor) as zf:
    zf.extractall("/var/files/extracted/")

Environment variable overrides

See the Default limits for reference.

All limits can be overridden without changing code:

export SAFEZIP_MAX_FILE_SIZE=104857600    # 100 MiB (default: 1 GiB)
export SAFEZIP_MAX_TOTAL_SIZE=524288000   # 500 MiB (default: 5 GiB)
export SAFEZIP_MAX_FILES=1000             # (default: 10 000)
export SAFEZIP_MAX_PER_MEMBER_RATIO=50    # (default: 200)
export SAFEZIP_MAX_TOTAL_RATIO=50         # (default: 200)
export SAFEZIP_MAX_NESTING_DEPTH=1        # (default: 3)
export SAFEZIP_SYMLINK_POLICY=ignore      # reject | ignore | resolve_internal (default: reject)

Default limits

Parameter	Default
max_file_size	1 GiB
max_total_size	5 GiB
max_files	10 000
max_per_member_ratio	200
max_total_ratio	200
max_nesting_depth	3
symlink_policy	REJECT
recursive	False

Testing

All tests run inside Docker to prevent accidental pollution of the host system:

make test

To test a specific Python version:

make test-env ENV=py312

Writing documentation

Keep the following hierarchy:

=====
title
=====

header
======

sub-header
----------

sub-sub-header
~~~~~~~~~~~~~~

sub-sub-sub-header
^^^^^^^^^^^^^^^^^^

sub-sub-sub-sub-header
++++++++++++++++++++++

sub-sub-sub-sub-sub-header
**************************

License

MIT

Support

For security issues contact me at the e-mail given in the Author section.

For overall issues, go to GitHub.

Author

Artur Barseghyan <[e-mail]>