CVE-2017-6740 in IOS
Summary
by MITRE
The Simple Network Management Protocol (SNMP) subsystem of Cisco IOS 12.0 through 12.4 and 15.0 through 15.6 and IOS XE 2.2 through 3.17 contains multiple vulnerabilities that could allow an authenticated, remote attacker to remotely execute code on an affected system or cause an affected system to reload. An attacker could exploit these vulnerabilities by sending a crafted SNMP packet to an affected system via IPv4 or IPv6. Only traffic directed to an affected system can be used to exploit these vulnerabilities. The vulnerabilities are due to a buffer overflow condition in the SNMP subsystem of the affected software. The vulnerabilities affect all versions of SNMP: Versions 1, 2c, and 3. To exploit these vulnerabilities via SNMP Version 2c or earlier, the attacker must know the SNMP read-only community string for the affected system. To exploit these vulnerabilities via SNMP Version 3, the attacker must have user credentials for the affected system. All devices that have enabled SNMP and have not explicitly excluded the affected MIBs or OIDs should be considered vulnerable. Cisco Bug IDs: CSCve66601.
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Analysis
by VulDB Data Team • 07/31/2025
The vulnerability identified as CVE-2017-6740 represents a critical buffer overflow condition within the Simple Network Management Protocol subsystem of Cisco IOS and IOS XE operating systems. This flaw affects a broad range of Cisco networking equipment including routers and switches running versions 12.0 through 12.4 and 15.0 through 15.6 of IOS, along with IOS XE versions 2.2 through 3.17. The vulnerability stems from inadequate input validation within the SNMP processing mechanisms, creating a potential entry point for malicious actors to execute arbitrary code or induce system reboots on affected devices.
The technical exploitation of this vulnerability requires an authenticated attacker who can send specially crafted SNMP packets to the target system over either IPv4 or IPv6 networks. This attack vector aligns with ATT&CK technique T1071.004 for application layer protocol usage and represents a network service exploitation scenario. The buffer overflow occurs within the SNMP subsystem's handling of incoming packets, specifically when processing certain MIB (Management Information Base) objects or OIDs (Object Identifiers). The vulnerability affects all SNMP versions including v1, v2c, and v3, though the authentication requirements vary based on the version used. For SNMP v2c and earlier versions, attackers must possess the correct read-only community string to successfully exploit the vulnerability, while SNMP v3 requires valid user credentials including authentication and privacy parameters.
The operational impact of CVE-2017-6740 extends beyond simple system disruption to potentially enable full system compromise. An attacker who successfully exploits this vulnerability could gain remote code execution privileges, allowing them to install backdoors, modify network configurations, or establish persistent access to the compromised device. The system reload capability provides an additional attack vector that could be used for denial of service attacks, disrupting network operations and potentially causing cascading failures across interconnected network infrastructure. This vulnerability directly maps to CWE-121, heap-based buffer overflow, and CWE-125, out-of-bounds read, representing fundamental memory safety issues that can lead to arbitrary code execution. The affected systems are particularly vulnerable because they typically run with elevated privileges and serve as critical network infrastructure components.
Organizations should implement immediate mitigations including disabling SNMP if not required for network management operations, implementing strict SNMP access controls with strong community strings, and applying the latest Cisco security patches. Network segmentation and monitoring solutions should be deployed to detect anomalous SNMP traffic patterns that might indicate exploitation attempts. The vulnerability affects all devices with enabled SNMP services that have not explicitly excluded the affected MIBs or OIDs, making comprehensive network inventory and configuration reviews essential. Additionally, implementing SNMPv3 with strong authentication and privacy parameters provides better protection against exploitation attempts, though the underlying buffer overflow issue requires proper software patching to fully remediate. Network administrators should also consider implementing intrusion detection systems that can identify and alert on suspicious SNMP packet structures that may indicate exploitation attempts.