CVE-2017-6739 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: CSCve66540.
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Analysis
by VulDB Data Team • 07/31/2025
The vulnerability described in CVE-2017-6739 represents a critical buffer overflow condition within the Simple Network Management Protocol subsystem of Cisco IOS and IOS XE software versions spanning from 12.0 through 12.4 and 15.0 through 15.6. This flaw exists across multiple software releases and affects all SNMP protocol versions including v1, v2c, and v3, making it particularly dangerous as it can be exploited through various authentication mechanisms. The vulnerability stems from improper input validation within the SNMP processing logic, creating a condition where crafted malicious packets can trigger memory corruption. According to CWE-121, this vulnerability manifests as a stack-based buffer overflow, where an attacker can overwrite adjacent memory locations and potentially execute arbitrary code on the affected system. The attack requires an authenticated remote connection, meaning that an attacker must first establish valid credentials to exploit the vulnerability, though the authentication requirements differ based on SNMP version used.
The operational impact of this vulnerability extends beyond simple code execution to include potential system reloads, effectively causing denial of service conditions that can disrupt network operations. The attack vector specifically requires sending malicious SNMP packets to the targeted device via IPv4 or IPv6 protocols, with the attacker needing access to the network segment where the vulnerable device resides. The exploitation process differs slightly between SNMP versions, with v2c and earlier requiring knowledge of the SNMP read-only community string, while SNMP v3 requires valid user credentials for authentication. This distinction demonstrates the layered nature of the vulnerability, where different authentication mechanisms provide varying levels of access control but all ultimately lead to the same exploitable buffer overflow condition. The fact that all versions of SNMP are affected indicates a fundamental flaw in the software's input handling rather than a version-specific implementation issue.
Cisco's identification of this vulnerability through Bug ID CSCve66540 highlights the severity of the issue and the need for immediate remediation. The affected devices are those that have SNMP enabled and have not explicitly excluded the vulnerable MIBs or OIDs, meaning that default configurations of Cisco network devices are at risk. This widespread impact across multiple IOS and IOS XE versions creates a significant challenge for network administrators who must assess and patch numerous devices across their network infrastructure. The vulnerability's classification under ATT&CK technique T1072 for Application Deployment, combined with T1059 for Command and Scripting Interpreter, indicates that successful exploitation could allow attackers to establish persistent access to network devices. Organizations should consider implementing network segmentation and access control lists to limit SNMP traffic to only trusted sources, as well as monitoring for unusual SNMP traffic patterns that might indicate exploitation attempts. The vulnerability's potential for remote code execution makes it particularly attractive to threat actors seeking to compromise network infrastructure and establish backdoor access points.
The technical flaw in the SNMP subsystem demonstrates how legacy protocols can contain fundamental security issues when integrated into modern network infrastructure. The buffer overflow condition represents a classic software vulnerability pattern that has been documented in numerous security advisories and represents a failure in input validation and memory management within the SNMP implementation. Network security teams should prioritize patching affected devices and implementing monitoring solutions that can detect the specific packet patterns associated with this vulnerability. The requirement for authentication, while providing some protection, does not eliminate the risk as SNMP community strings are often weak or default configurations that can be easily discovered through network scanning or social engineering. Organizations should also consider implementing SNMPv3 with strong authentication and encryption mechanisms as a mitigation strategy, though the vulnerability itself affects all SNMP versions, making comprehensive patching the most reliable solution.