what you don't know can hurt you

Serv-U FTP Server 15.1.6.25 Local Privilege Escalation

Serv-U FTP Server 15.1.6.25 Local Privilege Escalation
Posted May 30, 2019
Authored by Chris Moberly

Serv-U FTP Server version 15.1.6.25 suffers from a local privilege escalation vulnerability via authentication bypass.

tags | exploit, local
advisories | CVE-2018-19999
MD5 | 0fd8987096741b41281ea7394a04378a

Serv-U FTP Server 15.1.6.25 Local Privilege Escalation

Change Mirror Download
Issue:                  Local Privilege Escalation
CVE: CVE-2018-19999
Security researcher: Chris Moberly @ The Missing Link Security
Product name: Serv-U FTP Server
Product version: Tested on 15.1.6.25 (current as of Dec 2018)
Fixed in: 15.1.7

# Overview
The Serv-U FTP Server is vulnerable to authentication bypass leading to
privilege escalation in Windows operating environments due to broken access
controls. This can only be exploited by users who already have local access to
the Serv-U server.

By default, Serv-U runs in the context of 'SYSTEM' on Windows hosts. For
managing the environment, an executable is installed called "Serv-U". This
launches a dedicated UI when logged in to the machine via a graphical console.

What this application actually is, however, is a simple wrapper for
the HTTP interface. This can be confirmed by running Wireshark and listening
on the loopback interface. When the application first launches, a GET request
like the following can be observed:

```
GET /?Session=[REDACTED]&Language=en,US&LocalAdmin=1&Sync=68912515 HTTP/1.1
Host: 127.0.0.1:43958
Cookie: SULang=en%2CUS; domainname=test; domainid=; domainodbc=; 0UserGroupRadio=0
```

Note that the HTTP request above contains no logon credentials. This is met
with a reply like the following:

```
HTTP/1.0 200 OK
Server: Serv-U/15.1.6.25
Set-Cookie: Session=[REDACTED]; path=/; httponly;
Set-Cookie: CsrfToken=[REDACTED]; path=/; httponly;
Set-Cookie: SULang=en,US
```

The reply above can be seen to have a valid session token.

By default, low-privilege users cannot simply open the desktop application to
bypass a login prompt. However, while the management application is still
running, any user on the local machine can access the URL in the GET request
above and bypass authentication. In a default installation, this grants them
the highest level of access.

If an administrative user leaves the application running (either during active
use or something like a disconnected RDP session), this can be exploited.
Exploitation is possible by browsing to the following URL:

http://localhost/?Session=XXXXX&Language=en,US&LocalAdmin=1

The "Session" URL parameter must be brute-forced. This should be trivial.
Observed session IDs during limited tested were either 4 or 5 numerical digits.

Within this context, RCE (remote code execution) is a built-in feature. Simply
create an event on any user account with the details of the binary to run
and trigger the event manually as a test. This command will execute in the
context of the windows SYSTEM account, permitted a low privilege user to
take full control of the host operating system.

Sniffing the loopback interface on a target is NOT required, as this can be
done on a test machine under the attacker's control in order to enumerate the
vulnerability.

# Remediation
Serv-U administrators can do the following:
- Install the available hotfix from Serv-U.
- Set a password for the default Local Admin account. This must be done
manually, as it is not part of the installation options.
- Run the service as a lower-privileged account, which is not the default
installation option.


Comments

RSS Feed Subscribe to this comment feed

No comments yet, be the first!

Login or Register to post a comment

File Archive:

October 2019

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Oct 1st
    24 Files
  • 2
    Oct 2nd
    15 Files
  • 3
    Oct 3rd
    7 Files
  • 4
    Oct 4th
    4 Files
  • 5
    Oct 5th
    10 Files
  • 6
    Oct 6th
    1 Files
  • 7
    Oct 7th
    21 Files
  • 8
    Oct 8th
    19 Files
  • 9
    Oct 9th
    5 Files
  • 10
    Oct 10th
    20 Files
  • 11
    Oct 11th
    17 Files
  • 12
    Oct 12th
    4 Files
  • 13
    Oct 13th
    4 Files
  • 14
    Oct 14th
    15 Files
  • 15
    Oct 15th
    19 Files
  • 16
    Oct 16th
    25 Files
  • 17
    Oct 17th
    17 Files
  • 18
    Oct 18th
    0 Files
  • 19
    Oct 19th
    0 Files
  • 20
    Oct 20th
    0 Files
  • 21
    Oct 21st
    0 Files
  • 22
    Oct 22nd
    0 Files
  • 23
    Oct 23rd
    0 Files
  • 24
    Oct 24th
    0 Files
  • 25
    Oct 25th
    0 Files
  • 26
    Oct 26th
    0 Files
  • 27
    Oct 27th
    0 Files
  • 28
    Oct 28th
    0 Files
  • 29
    Oct 29th
    0 Files
  • 30
    Oct 30th
    0 Files
  • 31
    Oct 31st
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2019 Packet Storm. All rights reserved.

Services
Security Services
Hosting By
Rokasec
close