CVE-2017-3881 in IOS
Summary
by MITRE
A vulnerability in the Cisco Cluster Management Protocol (CMP) processing code in Cisco IOS and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a reload of an affected device or remotely execute code with elevated privileges. The Cluster Management Protocol utilizes Telnet internally as a signaling and command protocol between cluster members. The vulnerability is due to the combination of two factors: (1) the failure to restrict the use of CMP-specific Telnet options only to internal, local communications between cluster members and instead accept and process such options over any Telnet connection to an affected device; and (2) the incorrect processing of malformed CMP-specific Telnet options. An attacker could exploit this vulnerability by sending malformed CMP-specific Telnet options while establishing a Telnet session with an affected Cisco device configured to accept Telnet connections. An exploit could allow an attacker to execute arbitrary code and obtain full control of the device or cause a reload of the affected device. This affects Catalyst switches, Embedded Service 2020 switches, Enhanced Layer 2 EtherSwitch Service Module, Enhanced Layer 2/3 EtherSwitch Service Module, Gigabit Ethernet Switch Module (CGESM) for HP, IE Industrial Ethernet switches, ME 4924-10GE switch, RF Gateway 10, and SM-X Layer 2/3 EtherSwitch Service Module. Cisco Bug IDs: CSCvd48893.
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability described in CVE-2017-3881 represents a critical security flaw within Cisco's Cluster Management Protocol implementation across multiple IOS and IOS XE software versions. This issue specifically targets the handling of Telnet options within the CMP processing code, creating a pathway for remote attackers to gain unauthorized control over affected network devices. The vulnerability stems from fundamental design flaws in how the system processes cluster management communications, particularly when these communications are transmitted over standard Telnet connections that should normally be restricted to internal cluster member interactions.
The technical exploitation of this vulnerability relies on the combination of two distinct but interrelated flaws in the CMP processing mechanism. First, the system fails to properly restrict CMP-specific Telnet options to only internal communications between cluster members, allowing these options to be processed over any Telnet connection to the affected device. This represents a clear violation of the principle of least privilege and creates an unexpected attack surface. Second, the system incorrectly handles malformed CMP-specific Telnet options, which can trigger memory corruption or execution flow manipulation when processed by the vulnerable software. This dual-factor vulnerability creates a perfect storm where an attacker can send specially crafted malformed options that bypass normal security controls while simultaneously exploiting processing errors to achieve their objectives.
The operational impact of this vulnerability extends far beyond simple service disruption, as it can lead to complete device compromise with elevated privileges. An unauthenticated remote attacker who successfully exploits this vulnerability can achieve either a device reload that causes denial of service or gain the ability to execute arbitrary code with full system privileges. This capability allows attackers to completely take control of the affected device, potentially enabling them to modify network configurations, intercept traffic, or use the compromised device as a pivot point for further attacks within the network infrastructure. The affected devices include a wide range of Cisco switches and service modules, making this vulnerability particularly dangerous in enterprise network environments where these devices are commonly deployed.
The vulnerability affects multiple Cisco product lines including Catalyst switches, Embedded Service 2020 switches, various EtherSwitch Service Modules, IE Industrial Ethernet switches, ME 4924-10GE switches, RF Gateway 10 devices, and SM-X Layer 2/3 EtherSwitch Service Modules. This broad impact demonstrates the widespread nature of the flaw and suggests that organizations with legacy network infrastructure may be particularly vulnerable. From a cybersecurity perspective, this vulnerability aligns with CWE-248, which addresses "Uncaught Exception" conditions, and follows ATT&CK technique T1210 for "Exploitation of Remote Services" and T1068 for "Exploitation for Privilege Escalation." The attack vector specifically targets the Telnet service, making it a classic example of how legacy protocols can introduce security weaknesses when not properly secured or restricted.
Organizations affected by this vulnerability should immediately implement mitigations to prevent exploitation. The primary recommended approach involves restricting access to Telnet services and ensuring that CMP-specific Telnet options are only processed within trusted internal network segments. Network administrators should disable Telnet access where possible and implement stronger authentication mechanisms such as SSH for remote access. Additionally, applying the relevant Cisco IOS and IOS XE software updates that address the CMP processing flaws is essential for permanent remediation. The vulnerability's nature suggests that organizations should also conduct thorough network audits to identify all devices that may be running affected software versions and ensure that proper network segmentation prevents unauthorized access to these critical infrastructure components.