EUVD-2026-42396
GHSA-gjrg-mpp7-g774
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attacker-supplied archive extracted by a server-side library needs no auth or privileges (PR:N) at low complexity (AC:L); impact is availability-only (A:H, C/I:N).
Primary rating from Vendor (https://github.com/miurahr/py7zr).
CVSS VectorVendor: https://github.com/miurahr/py7zr
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
6Blast Radius
ecosystem impact- 363 pypi packages depend on py7zr (224 direct, 142 indirect)
Ecosystem-wide dependent count for version 1.1.3.
DescriptionCVE.org
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.
AnalysisAI
Denial-of-service via decompression bomb in py7zr, the pure-Python 7-Zip library, affects all versions up to and including 1.1.2. The library's Worker.decompress() writes extracted data to disk or memory without tracking cumulative decompressed size, so a tiny crafted .7z (demonstrated at a 6,556:1 ratio - 15.6 KB expanding to 100 MB) can exhaust disk or RAM on any application that extracts untrusted archives. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the target application uses py7zr <= 1.1.2 to extract a .7z archive the attacker controls or can supply (via upload, email attachment, shared storage, or any untrusted input path), and that no external OS/container resource limit already caps decompression output. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N, VA:H, VC:N/VI:N) scores 8.7 and correctly captures a low-complexity, no-privilege attack whose only impact is availability - despite the input Tags labeling this 'Information Disclosure,' which is inaccurate and should be disregarded (there is no confidentiality or integrity impact). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker uploads a ~15 KB .7z file to a service that uses py7zr to extract user-submitted archives (for example an antivirus scanner, document converter, or ingestion pipeline). When the server calls extractall(), py7zr expands the file to hundreds of megabytes or gigabytes with no size check, filling the disk or exhausting memory and taking the service offline. … |
| Remediation | Vendor-released patch: 1.1.3 - upgrade py7zr to >= 1.1.3 (e.g. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all applications and systems using py7zr versions 1.1.2 or earlier, prioritizing those that process untrusted or externally-supplied files. …
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View allVendor StatusVendor
SUSE
Severity: Moderate| Product | Status |
|---|---|
| openSUSE Tumbleweed | Fixed |
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