Tenable Research Advisory: Multiple Vulnerabilities Discovered in MikroTik's RouterOS

Tenable Research has discovered several vulnerabilities in RouterOS, an operating system used in MikroTik routers, the most critical of which would allow attackers to potentially gain full system access.

Tenable Research has discovered several vulnerabilities in RouterOS, an operating system used in MikroTik routers. Jacob Baines, the Tenable researcher who made the discovery, presented the talk "Bug Hunting in RouterOS" at Derbycon on October 7. The vulnerabilities include CVE-2018-1156 -- an authenticated remote code execution (RCE) -- as well as a file upload memory exhaustion (CVE-2018-1157), a www memory corruption (CVE-2018-1159) and a recursive parsing stack exhaustion (CVE-2018-1158). The most critical of these vulnerabilities is the authenticated RCE, which would allow attackers to potentially gain full system access. They were tested against RouterOS 6.42.3 (release date: 05-25-2018) using the x86 ISO.

• What do you need to know? Tenable Research has discovered multiple vulnerabilities in a proprietary operating system, RouterOS, used by MikroTik routers. The vulnerabilities include an authenticated RCE, a file upload memory exhaustion and a recursive parsing stack exhaustion.
• What’s the attack vector? Attackers could use default credentials, frequently left unchanged on routers, to exploit these vulnerabilities.
• What’s the business impact? The authenticated RCE vulnerability could be exploited with default credentials, granting an attacker full system access and allowing them to divert and reroute traffic or gain access to any internal system that uses the router.
• What’s the solution? MikroTik released RouterOS versions 6.40.9, 6.42.7 and 6.43 to address these vulnerabilities.

Background

RouterOS is an operating system based on the Linux kernel, which implements functionalities normally used by Internet Service Providers (ISPs), such as Border Gateway Protocol (BGP), IPv6, Open Shortest Path First (OSPF) or Multiprotocol Label Switching (MPLS). RouterOS, supported by MikroTik and its user community, provides a wide variety of configuration examples. RouterOS is embedded in MikroTik’s RouterBOARD product line, focused on small- and medium-sized internet access providers that typically provide broadband access in remote areas. MikroTik is headquartered in Riga, Latvia.

Based on Shodan analysis, there are hundreds of thousands of Mikrotik deployments worldwide, with strong concentrations in Brazil, Indonesia, China, the Russian Federation and India. As of October 3, 2018, approximately 35,000 - 40,000 devices display an updated, patched version.

Analysis

All of these vulnerabilities require authentication (essentially legitimate credentials). If the authenticated RCE vulnerability (CVE-2018-1156) is used against routers with default credentials, an attacker can potentially gain full system access, granting them the ability to divert and reroute traffic and gain access to any internal system that uses the router.

MikroTik routers were identified as being compromised by a Russian threat actor (APT28/Sofacy/FancyBear) in the recent VPNFilter malware, which received extensive media coverage. VPNFilter reportedly targets default credentials, the standard usernames and passwords enabled on the device out of the box, which users often leave unchanged. The actual vulnerabilities being used by VPNFilter are not fully known. Reports have stated that no zero-days were used, but this vulnerability could be a valid attack vector.

Proof of Concept

The licupgr binary has an sprintf that an authenticated user can use to trigger a stack buffer overflow. The sprintf is used on the following string:

GET /ssl_conn.php?usrname=%s&passwd=%s&softid=%s&level=%d&pay_typ'e=%d&board=%d HTTP/1.0

Where the user has control of the username and password strings, an authenticated user can exploit this to gain root access to the underlying system.

Solution

MikroTik released RouterOS versions 6.40.9, 6.42.7 and 6.43 to address these vulnerabilities. Users should also be sure to change the default credentials wherever possible.

Additional information:

• MikroTik Advisory
• Tenable Research Advisory
• Symantec Report on VPNFilter

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