Ubiquiti UniFi Video 3.7.3 - Local Privilege Escalation

RCE Security Advisory
https://www.rcesecurity.com


1. ADVISORY INFORMATION
=======================
Product:        Ubiquiti UniFi Video (Windows)
Vendor URL:     https://www.ubnt.com
Type:           Improper Handling of Insufficient Permissions or Privileges
                [CWE-280]
Date found:     2016-05-24
Date published: 2017-12-20
CVSSv3 Score:   7.8 (CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
CVE:            CVE-2016-6914


2. CREDITS
==========
This vulnerability was discovered and researched by Julien Ahrens from
RCE Security.


3. VERSIONS AFFECTED
====================
UniFi Video 3.7.3 (Windows),
UniFi Video 3.7.0 (Windows),
UniFi Video 3.2.2 (Windows),
older versions may be affected too.


4. INTRODUCTION
===============
UniFi Video is a powerful and flexible, integrated IP video management
surveillance system designed to work with Ubiquiti’s UniFi Video Camera product
line. UniFi Video has an intuitive, configurable, and feature‑packed user
interface with advanced features such as motion detection, auto‑discovery,
user-level security, storage management, reporting, and mobile device support.

(from the vendor's homepage)


5. VULNERABILITY DETAILS
========================
Ubiquiti UniFi Video for Windows is installed to "C:\ProgramData\unifi-video\"
by default and is also shipped with a service called "Ubiquiti UniFi Video". Its
executable "avService.exe" is placed in the same directory and also runs under
the NT AUTHORITY/SYSTEM account.

However the default permissions on the "C:\ProgramData\unifi-video" folder are
inherited from "C:\ProgramData" and are not explicitly overridden, which allows
all users, even unprivileged ones, to append and write files to the application
directory:

c:\ProgramData>icacls unifi-video
unifi-video NT AUTHORITY\SYSTEM:(I)(OI)(CI)(F)
BUILTIN\Administrators:(I)(OI)(CI)(F)
CREATOR OWNER:(I)(OI)(CI)(IO)(F)
BUILTIN\Users:(I)(OI)(CI)(RX)
BUILTIN\Users:(I)(CI)(WD,AD,WEA,WA)

Upon start and stop of the service, it tries to load and execute the file at
"C:\ProgramData\unifi-video\taskkill.exe". However this file does not exist in
the application directory by default at all.

By copying an arbitrary "taskkill.exe" to "C:\ProgramData\unifi-video\" as an
unprivileged user, it is therefore possible to escalate privileges and execute
arbitrary code as NT AUTHORITY/SYSTEM.


6. RISK
=======
To successfully exploit this vulnerability, an attacker must already have access
to a system running a vulnerable installation of UniFi video using a
low-privileged user account (i.e. through a password compromise).

The vulnerability allows local attackers to escalate privileges and execute
arbitrary code as NT AUTHORITY/SYSTEM, which basically means a complete loss of
the system's confidentiality, integrity as well as availability.


7. SOLUTION
===========
Update to v3.8.0


8. REPORT TIMELINE
==================
2016-05-24: Discovery of the vulnerability
2016-05-24: Reported to vendor via HackerOne (#140793)
2016-05-24: Vendor acknowledges the vulnerability
2016-08-22: Request for status update
2016-08-22: Vendor states that there is no update so far
2016-08-23: MITRE assigns CVE-2016-6914
2016-11-08: Request for status update
2016-11-08: Vendor states that there is no update so far
2016-12-08: Request for status update
2016-12-08: Vendor states that project team is working on it
2017-02-23: Request for status update
2017-03-23: No response from vendor
2017-03-23: Request for status update
2017-03-23: Vendor states that fix is scheduled for v3.7.0
2017-05-23: v3.7.0 was released, but vulnerability is still exploitable,
            vendor notified again
2017-06-07: Vendor states that fix is actually delayed
2017-08-26: Vendor provides beta versions of 3.7.3 and 3.8.0-beta3, which should
            fix the issue
2017-08-31: While v3.7.3 is still vulnerable, the issue was fixed in 3.8.0-beta3
2017-09-18: v3.8.0 released publicly
2017-12-20: Public disclosure


9. REFERENCES
=============
http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=2016-6914
https://hackerone.com/reports/140793