FortiGate SSL VPN Portal 5.x Cross Site Scripting

FortiGate SSL VPN Portal versions 5.6.2 and below, 5.4.6 and below, 5.2.12 and below, and 5.0 and below suffer from a cross site scripting vulnerability.

MD5 | 326f6888433930a05fa0eaf4edd6db42

SEC Consult Vulnerability Lab Security Advisory < 20171129-0 >
title: FortiGate SSL VPN Portal XSS Vulnerability
product: Fortinet FortiOS
vulnerable version: see: Vulnerable / tested versions
fixed version: see: Solution
CVE number: CVE-2017-14186
impact: Medium
found: 2017-10-02
by: Stefan Viehböck (Office Vienna)
SEC Consult Vulnerability Lab

An integrated part of SEC Consult
Bangkok - Berlin - Linz - Montreal - Moscow
Singapore - Vienna (HQ) - Vilnius - Zurich


Vendor description:
"From the start, the Fortinet vision has been to deliver broad, truly
integrated, high-performance security across the IT infrastructure.

We provide top-rated network and content security, as well as secure access
products that share intelligence and work together to form a cooperative
fabric. Our unique security fabric combines Security Processors, an intuitive
operating system, and applied threat intelligence to give you proven security,
exceptional performance, and better visibility and control--while providing
easier administration."


Vulnerability overview/description:
The FortiGate SSL VPN Portal is prone to a reflected cross-site scripting (XSS)
vulnerability. The HTTP GET parameter "redir" is vulnerable.
An attacker can exploit this vulnerability by tricking a victim to visit a URL.
The attacker is able to hijack the session of the attacked user, and use this
vulnerability in the course of spear-phishing attacks, e.g. by displaying a
login prompt that sends credentials of victim back to the attacker.

Note: This vulnerability is also an open redirect and is very similar to a
vulnerability that was fixed in FortiOS in March 2016 (FG-IR-16-004).

Proof of concept:
The following request exploits the issue:

The server responds with a page that looks as follows:
<script language="javascript">

Vulnerable / tested versions:
FortiOS 5.6.0 -> 5.6.2
FortiOS 5.4.0 -> 5.4.6
FortiOS 5.2.0 -> 5.2.12
FortiOS 5.0 and below

More information can be found at:

Vendor contact timeline:
2017-10-02: Contacting vendor through [email protected]
2017-10-03: Vendor confirms vulnerability, assigns CVE-2017-14186. Expected fix in
version 5.6.3
2017-11-23: Vendor provides update
2017-11-29: Coordinated public release of advisory

FortiOS 5.6 branch: Upgrade to upcoming 5.6.3 (ETA: November 27th)
FortiOS 5.4 branch: Upgrade to 5.4.6 special build (*) or upcoming 5.4.7 (ETA Dec
FortiOS 5.2 branch: Upgrade to 5.2.12 special build (*) or upcoming 5.2.13 (ETA:
Dec 14th)

More information can be found at:

Not available.

Advisory URL:


SEC Consult Vulnerability Lab

SEC Consult
Bangkok - Berlin - Linz - Montreal - Moscow
Singapore - Vienna (HQ) - Vilnius - Zurich

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It
ensures the continued knowledge gain of SEC Consult in the field of network
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

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EOF Stefan Viehböck / @2017

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