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	"title": "Evolution of attacks on Cisco IOS devices",
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	"plain_text": "Evolution of attacks on Cisco IOS devices\r\nBy Graham Holmes,\r\nPublished: 2015-10-08 · Archived: 2026-04-05 14:37:18 UTC\r\nWhile “SYNful Knock” is the latest identified malware targeting Cisco devices running Cisco IOS, we have\r\nidentified and investigated six other malware incidents during the last four years that target Cisco devices running\r\nCisco IOS. The nature of threats is evolving and Cisco will continue to adapt technology delivering trustworthy\r\nsolutions that our customers can rely on. This also means that customers will need to evolve, fully utilizing the\r\nsecurity tools that are available, as well as ensuring security best practices are in place.\r\nThe malware used in these evolved Cisco IOS attacks show increasing levels of complexity in the type of\r\nmodifications made to Cisco IOS, the behavior of its Command and Control (C\u0026C) network (when present), and\r\nthe platforms they target.\r\nBefore talking about specifics of each investigated malware incident, it is important to note that in all cases, no\r\nevidence has been found that attackers exploited a previously known or unknown vulnerability to install the\r\nmalware. All available data points suggest either the use of compromised administrator credentials or physical\r\naccess to the devices or images.\r\nThe following table and associated description provides a brief overview of the malware samples, as well as an\r\noverview of the actions that Cisco took in response to those findings. The source of this information is internal\r\nanalysis performed by Cisco forensics teams.\r\nNotes to table:\r\nhttps://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices\r\nPage 1 of 5\n\nINFECTION METHOD: Static means “modifications to the IOS binary stored in the device’s flash”, Runtime\r\nmeans “modifications performed to the runtime memory code without changes to the IOS binary in flash”\r\nREMOTE DETECTABILITY: refers to the means to remotely look for the presence of the malware on a\r\ncompromised system through scanning systems and signatures. Other means of detecting modifications through\r\nmemory analysis is possible in all cases.\r\nIncidents 0 and 1\r\nThe first two incidents were detected in 2011 and 2012 respectively, and were most likely custom malware\r\ntargeting a specific victim. Those incidents were very basic (from a technical point of view) and involve binary\r\npatches to a Cisco IOS image. They allowed the modified IOS image file to be installed on the target routers\r\n(C3825, C2800nm, and C3845). Devices affected were in the Cisco 2800 and 3800 family of routers. No other\r\nCisco devices were identified as affected by this malware.\r\nThe modification essentially affects the Diffie-Hellman key exchange protocol in order to weaken the derived\r\nkeying material. The result is that with casual inspection the encrypted traffic seems unmodified, but the effect is\r\nthat an attacker could decrypt protected traffic with less effort than would normally be required.\r\nPlatforms implementing Trust Anchor technologies and signed binaries would not be affected by either one of\r\nthose two malware examples.\r\nIncidents 2 and 3\r\nTwo new malware samples were identified in 2013, both targeting the Cisco 7600 series of devices. In both cases,\r\nthe attacker leveraged compromised administrator credentials to modify the in-memory copy of the Cisco IOS\r\ncode, using debugging and troubleshooting Cisco IOS command line interface (CLI) commands.\r\nThe primary purpose of the added code appears to be exfiltration of IPv4 packets that match criteria set by the\r\nattacker. The targeted traffic is copied and those packets are then forwarded to a specified IP address that is under\r\nthe control of the attacker. A secondary purpose is to provide NAT (Network Address Translation) capabilities, so\r\nan attacker is able to access an IPv4 address within a compromised network that would normally not be reachable\r\nfrom the public Internet (ie: devices using RFC-1918 addresses).\r\nSince both of these malware samples involved the modification of the in-memory code for Cisco IOS, neither\r\nTrust Anchor technologies nor image validation features would have detected or prevented the attack. But,\r\nbecause the modifications were performed on the in-memory copy of Cisco IOS, neither attack would achieve\r\npersistency across device reloads.\r\nIncident 3 has only been detected in a single customer network. It was discovered while troubleshooting crashes\r\non line cards on installed Cisco 7600 devices. Forensic analysis of the associated core dumps found that this attack\r\nused a C\u0026C mechanism similar to Incident 2 to provide the malware with instructions for data exfiltration. What\r\nis unique in this incident is targeting of multi-architecture line cards – something we have not seen in any other\r\nmalware analyzed as of this writing.\r\nhttps://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices\r\nPage 2 of 5\n\nIn both cases, the modifications were made to the in-memory copy of the executable code for the Cisco IOS image\r\n(with no changes to the actual binary Cisco IOS image in flash). The use of signed Cisco IOS images would not be\r\na defense. It does, however, highlight the need for strong protection of administrative credentials and authorization\r\nmechanisms for privileged access to any network device.\r\nIncident 4\r\nIncident 4 was discovered in late 2014 and affected Cisco 1800, Cisco 3800 and Cisco 7200 devices. Like the\r\nmalware seen in Incidents 2 and 3, the attack leveraged compromised administrative credentials to gain access to\r\ntarget devices for the purpose of installing the malware.\r\nThis malware, however, showed an increase in complexity compared to previous malware analyzed. It is the only\r\nanalyzed malware so far that is capable of persistence through both device reload as well as through Cisco IOS\r\nsoftware upgrades.\r\nThe malware has two separate components:\r\nAn initial infection, where the ROMMON on the targeted Cisco device is modified to ensure persistence of\r\nthe C\u0026C channel;\r\nA secondary infection occurs when the ROMMON is used to inject binary code into the in-memory Cisco\r\nIOS image to support data exfiltration.\r\nNote: This malware does not modify the binary Cisco IOS image in flash.\r\nThe ROMMON component of the malware handles the C\u0026C messages, which are embedded within the payload\r\nof ICMP packets delivered through the IPv4 protocol.\r\nThe secondary infection component is highly modular, and supports the loading and unloading of optional\r\n“modules,” which are delivered to the device through the C\u0026C channel. One of the observed modules purpose is\r\nto exfiltrate device-specific data via ICMP packets. This module creates an ICMP Echo Request packet with the\r\ndata to be exfiltrated as its payload. Other modules provide NAT capabilities, so C\u0026C messages can reach devices\r\nthat would otherwise not be accessible from the public Internet, and additional exfiltration capabilities for other\r\ntraffic defined by the attacker.\r\nLike Incident 3, the use of signed IOS images would not prevent this attack, as the binary Cisco IOS image stored\r\nin flash is never modified. However, the ROMMON compromise (used to achieve persistence between reloads\r\nand Cisco IOS software upgrades) would not be successful with current devices that incorporate secure boot, trust\r\nanchor modules, and image signing capabilities.\r\nIncident 5 (SYNful Knock)\r\nThe last example (known as SYNful Knock and jointly disclosed by Cisco and Mandiant’s FireEye), uses the\r\nsame static modifications to the Cisco IOS binary seen in Incidents 0 and 1. It also uses a C\u0026C approach similar\r\nto the one observed in Incident 2, but uses TCP instead of ICMP for C\u0026C traffic (hence the name SYNful Knock).\r\nSYNful Knock (like malware #0, #1, #2 and #3) CANNOT survive the installation of a known good Cisco IOS\r\nbinary image, obtained from a known, trusted source and verified to have the correct hash values.\r\nhttps://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices\r\nPage 3 of 5\n\nCisco actions to prevent and detect attacks against Cisco devices\r\nSince 2008, the Cisco Secure Development Lifecycle framework has provided development teams with standards\r\nand requirements to build products designed with protection features and capabilities. Boot time and run time\r\nsecurity features, such as Trust Anchor modules, secure boot, and memory protection are standard requirements.\r\nThe goal of these features is to protect customers from remote code injection attacks or static modifications to\r\nCisco IOS binary images.\r\nAs soon as the first malware was detected “in the wild,” forensics and analysis teams at Cisco began accelerating\r\nthe development of detection capabilities. We’ve developed forensics tools that can quickly validate the\r\nauthenticity of IOS images from core dumps or in-memory images. These are key tools used in incident response\r\nto help our customers confirm whether there is a compromise and the extent of such a compromise.\r\nConcurrently with the development of such forensics tools, we implemented measures to further ensure our supply\r\nchain integrity: verifying Cisco IOS image integrity through development, compilation, testing and release, and all\r\nthe way to distribution points. As part of those efforts, we recently introduced and began posting SHA-512 hash\r\nvalues for any Cisco image to further increase customer confidence on their image authenticity. These are\r\navailable for customer download on www.cisco.com.\r\nWe have also posted instructions and guidance for customers to harden their router authentication, authorization\r\nand accounting process and for validating Cisco IOS binary images already installed or to be installed on their\r\nCisco devices.\r\nWe’ve deployed tools that automatically analyze core dumps provided by customers to the Cisco Technical\r\nAssistance Center (TAC) as part of a Service Request. These tools automatically detect modifications to Cisco\r\nIOS images. They also detect malicious and/or counterfeit images by analyzing binary images installed on any\r\nCisco device that come through our RMA process.\r\nWe have reviewed all Cisco IOS command line interface (CLI) commands, and have removed commands that\r\nprovide limited value to customers during normal device operation, but could be misused by attackers with access\r\nto the device CLI.\r\nWe are in the pilot phase of an image validation service that offers customers the ability to quickly and\r\nautomatically analyze and detect modified Cisco IOS images running on their Cisco devices.\r\nWe have released SNORT and Yara signatures that detect SYNful Knock malware.\r\nWe have worked with all customers to quickly address their concerns or help them validate the running images in\r\ntheir network have not been compromised.\r\nWhat Can You Do?\r\nWe have published several documents that can be used by Cisco customers wanting to better understand how to\r\nprotect their Cisco IOS devices, harden their device configurations (including credential management procedures),\r\nand verify binary or in-memory running Cisco IOS images. The following are some of the resources you can find\r\non www.cisco.com:\r\nhttps://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices\r\nPage 4 of 5\n\nCisco IOS Software Integrity Assurance\r\nCisco Guide to Harden IOS Devices\r\nTelemetry-Based Infrastructure Device Integrity Monitoring\r\nTrust Anchor Technologies on Cisco products\r\nWhile some of the previously listed measures have been reactive, we are also taking active steps in developing\r\nnew capabilities to meet the challenges of an ever changing threat landscape. In terms of the attack continuum –\r\nprotect, detect, recover – Cisco has focused for many years on addressing the challenges of protecting our\r\nproducts through hardening, resiliency, and security capabilities.   We will continue and even accelerate those\r\nefforts, while also rapidly developing and adding detection and recovery capabilities to our products in the\r\nmedium and long term.\r\nThe challenge is clear: the nature of the threat to our customers is ever evolving. Cisco will continue to focus on\r\nproviding trustworthy solutions that our customers can rely on in this changing landscape.\r\nSource: https://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices\r\nhttps://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices\r\nPage 5 of 5",
	"extraction_quality": 1,
	"language": "EN",
	"sources": [
		"MITRE"
	],
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		"https://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices"
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