[CAVO] Fwd: Fwd: TA16-250A: The Increasing Threat to Network Infrastructure Devices and Recommended Mitigations

[Brent Turner]

[image: U.S. Department of Homeland Security US-CERT]

National Cyber Awareness System:


TA16-250A: The Increasing Threat to Network Infrastructure Devices and
Recommended Mitigations <https://www.us-cert.gov/ncas/alerts/TA16-250A>
09/06/2016 06:29 PM EDT

Original release date: September 06, 2016 | Last revised: September 28, 2016
Systems Affected

Network Infrastructure Devices

Overview

The advancing capabilities of organized hacker groups and cyber adversaries
create an increasing global threat to information systems. The rising
threat levels place more demands on security personnel and network
administrators to protect information systems. Protecting the network
infrastructure is critical to preserve the confidentiality, integrity, and
availability of communication and services across an enterprise.

To address threats to network infrastructure devices, this Alert provides
information on recent vectors of attack that advanced persistent threat
(APT) actors are targeting, along with prevention and mitigation
recommendations.

Description

Network infrastructure consists of interconnected devices designed to
transport communications needed for data, applications, services, and
multi-media. Routers and firewalls are the focus of this alert; however,
many other devices exist in the network, such as switches, load-balancers,
intrusion detection systems, etc. Perimeter devices, such as firewalls and
intrusion detection systems, have been the traditional technologies used to
secure the network, but as threats change, so must security strategies.
Organizations can no longer rely on perimeter devices to protect the
network from cyber intrusions; organizations must also be able to contain
the impact/losses within the internal network and infrastructure.

For several years now, vulnerable network devices have been the
attack-vector of choice and one of the most effective techniques for
sophisticated hackers and advanced threat actors. In this environment,
there has never been a greater need to improve network infrastructure
security. Unlike hosts that receive significant administrative security
attention and for which security tools such as anti-malware exist, network
devices are often working in the background with little oversight—until
network connectivity is broken or diminished. Malicious cyber actors take
advantage of this fact and often target network devices. Once on the
device, they can remain there undetected for long periods. After an
incident, where administrators and security professionals perform forensic
analysis and recover control, a malicious cyber actor with persistent
access on network devices can reattack the recently cleaned hosts. For this
reason, administrators need to ensure proper configuration and control of
network devices.
Proliferation of Threats to Information Systems *SYNful Knock*

In September 2015, an attack known as SYNful Knock was disclosed. SYNful
Knock silently changes a router’s operating system image, thus allowing
attackers to gain a foothold on a victim’s network. The malware can be
customized and updated once embedded. When the modified malicious image is
uploaded, it provides a backdoor into the victim’s network. Using a crafted
TCP SYN packet, a communication channel is established between the
compromised device and the malicious command and control (C2) server. The
impact of this infection to a network or device is severe and most likely
indicates that there may be additional backdoors or compromised devices on
the network. This foothold gives an attacker the ability to maneuver and
infect other hosts and access sensitive data.

The initial infection vector does not leverage a zero-day vulnerability.
Attackers either use the default credentials to log into the device or
obtain weak credentials from other insecure devices or communications. The
implant resides within a modified IOS image and, when loaded, maintains its
persistence in the environment, even after a system reboot. Any further
modules loaded by the attacker will only exist in the router’s volatile
memory and will not be available for use after the device reboots. However,
these devices are rarely or never rebooted.

To prevent the size of the image from changing, the malware overwrites
several legitimate IOS functions with its own executable code. The attacker
examines the functionality of the router and determines functions that can
be overwritten without causing issues on the router. Thus, the overwritten
functions will vary upon deployment.

The attacker can utilize the secret backdoor password in three different
authentication scenarios. In these scenarios the implant first checks to
see if the user input is the backdoor password. If so, access is granted.
Otherwise, the implanted code will forward the credentials for normal
verification of potentially valid credentials. This generally raises the
least amount of suspicion. Cisco has provided an alert on this attack
vector. For more information, see the Cisco SYNful Knock Security Advisory
<https://www.cisco.com/c/en/us/about/security-center/event-response/synful-knock.html>
.

Other attacks against network infrastructure devices have also been
reported, including more complicated persistent malware that silently
changes the firmware on the device that is used to load the operating
system so that the malware can inject code into the running operating
system. For more information, please see Cisco's description of the
evolution of attacks on Cisco IOS devices
<https://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices>
.
*Cisco Adaptive Security Appliance (ASA)*

A Cisco ASA device is a network device that provides firewall and Virtual
Private Network (VPN) functionality. These devices are often deployed at
the edge of a network to protect a site’s network infrastructure, and to
give remote users access to protected local resources.

In June 2016, NCCIC received several reports of compromised Cisco ASA
devices that were modified in an unauthorized way. The ASA devices directed
users to a location where malicious actors tried to socially engineer the
users into divulging their credentials.

It is suspected that malicious actors leveraged CVE-2014-3393
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2014-3393>to inject
malicious code into the affected devices. The malicious actor would then be
able to modify the contents of the Random Access Memory Filing System
(RAMFS) cache file system and inject the malicious code into the
appliance’s configuration. Refer to the Cisco Security Advisory Multiple
Vulnerabilities in Cisco ASA Software
<https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20141008-asa>for
more information and for remediation details.

In August 2016, a group known as “Shadow Brokers” publicly released a large
number of files, including exploitation tools for both old and newly
exposed vulnerabilities. Cisco ASA devices were found to be vulnerable to
the released exploit code. In response, Cisco released an update to address
a newly disclosed Cisco ASA Simple Network Management Protocol (SNMP)
remote code execution vulnerability (CVE-2016-6366
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-6366>). In
addition, one exploit tool targeted a previously patched Cisco
vulnerability (CVE-2016-6367
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-6367>). Although
Cisco provided patches <https://blogs.cisco.com/security/shadow-brokers> to
fix this Cisco ASA command-line interface (CLI) remote code execution
vulnerability in 2011, devices that remain unpatched are still vulnerable
to the described attack. Attackers may target vulnerabilities for months or
even years after patches become available.
Impact

If the network infrastructure is compromised, malicious hackers or
adversaries can gain full control of the network infrastructure enabling
further compromise of other types of devices and data and allowing traffic
to be redirected, changed, or denied. Possibilities of manipulation include
denial-of-service, data theft, or unauthorized changes to the data.

Intruders with infrastructure privilege and access can impede productivity
and severely hinder re-establishing network connectivity. Even if other
compromised devices are detected, tracking back to a compromised
infrastructure device is often difficult.

Malicious actors with persistent access to network devices can reattack and
move laterally after they have been ejected from previously exploited hosts.

Solution 1.    Segregate Networks and Functions

Proper network segmentation is a very effective security mechanism to
prevent an intruder from propagating exploits or laterally moving around an
internal network. On a poorly segmented network, intruders are able to
extend their impact to control critical devices or gain access to sensitive
data and intellectual property. Security architects must consider the
overall infrastructure layout, segmentation, and segregation. Segregation
separates network segments based on role and functionality. A securely
segregated network can contain malicious occurrences, reducing the impact
from intruders, in the event that they have gained a foothold somewhere
inside the network.
*Physical Separation of Sensitive Information*

Local Area Network (LAN) segments are separated by traditional network
devices such as routers. Routers are placed between networks to create
boundaries, increase the number of broadcast domains, and effectively
filter users’ broadcast traffic. These boundaries can be used to contain
security breaches by restricting traffic to separate segments and can even
shut down segments of the network during an intrusion, restricting
adversary access.
Recommendations:

   - Implement Principles of Least Privilege and need-to-know when
   designing network segments.
   - Separate sensitive information and security requirements into network
   segments.
   - Apply security recommendations and secure configurations to all
   network segments and network layers.

*Virtual Separation of Sensitive Information        *

As technologies change, new strategies are developed to improve IT
efficiencies and network security controls. Virtual separation is the
logical isolation of networks on the same physical network. The same
physical segmentation design principles apply to virtual segmentation but
no additional hardware is required. Existing technologies can be used to
prevent an intruder from breaching other internal network segments.
Recommendations:

   - Use Private Virtual LANs to isolate a user from the rest of the
   broadcast domains.
   - Use Virtual Routing and Forwarding (VRF) technology to segment network
   traffic over multiple routing tables simultaneously on a single router.
   - Use VPNs to securely extend a host/network by tunneling through public
   or private networks.


2.    Limit Unnecessary Lateral Communications

Allowing unfiltered workstation-to-workstation communications (as well as
other peer-to-peer communications) creates serious vulnerabilities, and can
allow a network intruder to easily spread to multiple systems. An intruder
can establish an effective “beach head” within the network, and then spread
to create backdoors into the network to maintain persistence and make it
difficult for defenders to contain and eradicate.
Recommendations:

   - Restrict communications using host-based firewall rules to deny the
   flow of packets from other hosts in the network. The firewall rules can be
   created to filter on a host device, user, program, or IP address to limit
   access from services and systems.
   - Implement a VLAN Access Control List (VACL), a filter that controls
   access to/from VLANs. VACL filters should be created to deny packets the
   ability to flow to other VLANs.
   - Logically segregate the network using physical or virtual separation
   allowing network administrators to isolate critical devices onto network
   segments.


3.    Harden Network Devices

A fundamental way to enhance network infrastructure security is to
safeguard networking devices with secure configurations. Government
agencies, organizations, and vendors supply a wide range of resources to
administrators on how to harden network devices. These resources include
benchmarks and best practices. These recommendations should be implemented
in conjunction with laws, regulations, site security policies, standards,
and industry best practices. These guides provide a baseline security
configuration for the enterprise that protects the integrity of network
infrastructure devices. This guidance supplements the network security best
practices supplied by vendors.
Recommendations:

   - Disable unencrypted remote admin protocols used to manage network
   infrastructure (e.g., Telnet, FTP).
   - Disable unnecessary services (e.g. discovery protocols, source
   routing, HTTP, SNMP, BOOTP).
   - Use SNMPv3 (or subsequent version) but do not use SNMP community
   strings.
   - Secure access to the console, auxiliary, and VTY lines.
   - Implement robust password policies and use the strongest password
   encryption available.
   - Protect router/switch by controlling access lists for remote
   administration.
   - Restrict physical access to routers/switches.
   - Backup configurations and store offline. Use the latest version of the
   network device operating system and update with all patches.
   - Periodically test security configurations against security
   requirements.
   - Protect configuration files with encryption and/or access controls
   when sending them electronically and when they are stored and backed up.


4.    Secure Access to Infrastructure Devices

Administrative privileges on infrastructure devices allow access to
resources that are normally unavailable to most users and permit the
execution of actions that would otherwise be restricted. When administrator
privileges are improperly authorized, granted widely, and/or not closely
audited, intruders can exploit them. These compromised privileges can
enable adversaries to traverse a network, expanding access and potentially
allowing full control of the infrastructure backbone. Unauthorized
infrastructure access can be mitigated by properly implementing secure
access policies and procedures.
Recommendations:

   - Implement Multi-Factor Authentication – Authentication is a process to
   validate a user’s identity. Weak authentication processes are commonly
   exploited by attackers. Multi-factor authentication uses at least two
   identity components to authenticate a user’s identity. Identity components
   include something the user knows (e.g., password); an object the user has
   possession of (e.g., token); and a trait unique to the specific person
   (e.g., biometric).
   - Manage Privileged Access – Use an authorization server to store access
   information for network device management. This type of server will enable
   network administrators to assign different privilege levels to users based
   on the principle of least privilege. When a user tries to execute an
   unauthorized command, it will be rejected. To increase the strength and
   robustness of user authentication, implement a hard token authentication
   server in addition to the AAA server, if possible. Multi-factor
   authentication increases the difficulty for intruders to steal and reuse
   credentials to gain access to network devices.
   - Manage Administrative Credentials – Although multi-factor
   authentication is highly recommended and a best practice, systems that
   cannot meet this requirement can at least improve their security level by
   changing default passwords and enforcing complex password policies. Network
   accounts must contain complex passwords of at least 14 characters from
   multiple character domains including lowercase, uppercase, numbers, and
   special characters. Enforce password expiration and reuse policies. If
   passwords are stored for emergency access, keep these in a protected
   off-network location, such as a safe.


5.    Perform Out-of-Band Management

Out-of-Band (OoB) management uses alternate communication paths to remotely
manage network infrastructure devices. These dedicated paths can vary in
configuration to include anything from virtual tunneling to physical
separation. Using OoB access to manage the network infrastructure will
strengthen security by limiting access and separating user traffic from
network management traffic. OoB management provides security monitoring and
can implement corrective actions without allowing the adversary who may
have already compromised a portion of the network to observe these changes.

OoB management can be implemented physically or virtually, or through a
hybrid of the two. Building additional physical network infrastructure is
the most secure option for the network managers, although it can be very
expensive to implement and maintain. Virtual implementation is less costly,
but still requires significant configuration changes and administration. In
some situations, such as access to remote locations, virtual encrypted
tunnels may be the only viable option.
Recommendations:

   - Segregate standard network traffic from management traffic.
   - Enforce that management traffic on devices only comes from the OoB.
   - Apply encryption to all management channels.
   - Encrypt all remote access to infrastructure devices such as terminal
   or dial-in servers.
   - Manage all administrative functions from a dedicated host (fully
   patched) over a secure channel, preferably on the OoB.
   - Harden network management devices by testing patches, turning off
   unnecessary services on routers and switches, and enforcing strong password
   policies. Monitor the network and review logs Implement access controls
   that only permit required administrative or management services (SNMP, NTP
   SSH, FTP, TFTP).


6.    Validate Integrity of Hardware and Software

Products purchased through unauthorized channels are often known as
“counterfeit,” “secondary,” or “grey market” devices. There have been
numerous reports in the press regarding grey market hardware and software
being introduced into the marketplace. Grey market products have not been
thoroughly tested to meet quality standards and can introduce risks to the
network. Lack of awareness or validation of the legitimacy of hardware and
software presents a serious risk to users’ information and the overall
integrity of the network environment. Products purchased from the secondary
market run the risk of having the supply chain breached, which can result
in the introduction of counterfeit, stolen, or second-hand devices. This
could affect network performance and compromise the confidentiality,
integrity, or availability of network assets. Furthermore, breaches in the
supply chain provide an opportunity for malicious software or hardware to
be installed on the equipment. In addition, unauthorized or malicious
software can be loaded onto a device after it is in operational use, so
integrity checking of software should be done on a regular basis.
Recommendations:

   - Maintain strict control of the supply chain; purchase only from
   authorized resellers.
   - Require resellers to implement a supply chain integrity check to
   validate hardware and software authenticity.
   - Inspect the device for signs of tampering.
   - Validate serial numbers from multiple sources.
   - Download software, updates, patches, and upgrades from validated
   sources.
   - Perform hash verification and compare values against the vendor’s
   database to detect unauthorized modification to the firmware.
   - Monitor and log devices, verifying network configurations of devices
   on a regular schedule.
   - Train network owners, administrators, and procurement personnel to
   increase awareness of grey market devices.


*Shadow Broker Exploits*
*Vendor* *CVE* *Exploit Name* *Vulnerability*
Fortinet CVE-2016-6909
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-6909>
EGREGIOUSBLUNDER Authentication cookie overflow
WatchGuard    CVE-2016-7089
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-7089>
ESCALATEPLOWMAN Command line injection via ipconfig
Cisco CVE-2016-6366
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-6366>
EXTRABACON SNMP
remote code execution
Cisco CVE-2016-6367
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-6367>
EPICBANANA Command
line injection remote code execution
Cisco CVE-2016-6415
<https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-6415>
BENIGNCERTAIN/PIXPOCKET    Information/memory leak
TOPSEC N/A ELIGIBLEBACHELOR Attack vector unknown, but has an XML-like
payload
beginning with <?tos length="001e.%8.8x"?
TOPSEC N/A ELIGIBLEBOMBSHELL HTTP cookie command injection
TOPSEC N/A ELIGIBLECANDIDATE HTTP cookie command injection
TOPSEC N/A ELIGIBLECONTESTANT HTTP POST parameter injection



References

   - Cisco SYNful Knock Security Advisory
   <http://www.cisco.com/c/en/us/about/security-center/event-response/synful-knock.html>
   - Cisco Security Advisory Multiple Vulnerabilities in Cisco ASA Software
   <https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20141008-asa>
   - Cisco Evolution of Attacks on Cisco IOS Devices
   <https://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices>
   - Cisco IOS Software Integrity Assurance
   <https://cisco.com/c/en/us/about/security-center/integrity-assurance.html>
   - Information Assurance Advisory NO. IAA U/OO/802097-16 Mitigate
   Unauthorized Cisco ROMMON
   <https://www.iad.gov/iad/library/ia-advisories-alerts/recommendations-to-mitigate-unauthorized-cisco-rommon-access-and-validate-boot-roms.cfm>
   - Information Assurance Advisory NO. IAA U/OO/802488-16 Vulnerabilities
   in Cisco Adaptive Security Appliances
   <https://www.iad.gov/iad/library/ia-advisories-alerts/vulnerability-in-cisco-adaptive-security-appliances-identified-in-open-source-v1.cfm>
   - Information Assurance Directorate Network Mitigations Package –
   Infrastructure
   <https://www.iad.gov/iad/library/ia-guidance/security-tips/network-mitigations-package-infrastructure.cfm>
   - Cisco Guide to Securing Cisco NX-OS Software Devices
   <https://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9402/guide_c07-665160.html>
   - Cisco Guide to Harden Cisco IOS XR Devices
   <https://cisco.com/web/about/security/intelligence/CiscoIOSXR.html>
   - Cisco Guide to Harden Cisco IOS Devices
   <https://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080120f48.shtml>
   - Cisco: A Framework to Protect Data Through Segmentation
   <https://www.cisco.com/c/en/us/about/security-center/framework-segmentation.html>

Revision History

   - September 6, 2016: Initial release
   - September 13, 2016: Added additional references

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