CVE-2017-6738 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: CSCve89865, CSCsy56638.
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Analysis
by VulDB Data Team • 07/31/2025
The vulnerability identified as CVE-2017-6738 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 in the SNMP processing logic where insufficient input validation allows maliciously crafted packets to trigger memory corruption. The vulnerability affects all SNMP versions including v1, v2c, and v3, making it particularly concerning as it encompasses the entire SNMP ecosystem. The buffer overflow occurs during packet processing when the system fails to properly validate the length of incoming SNMP messages before copying them into fixed-size buffers. This condition creates an opportunity for arbitrary code execution or system reload, depending on the specific exploitation vector and attack parameters. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which directly maps to the fundamental memory corruption principles that enable remote code execution in network services. The attack requires an authenticated remote attacker with network access to the target system, as the exploit must be delivered via crafted SNMP packets over IPv4 or IPv6 protocols.
The operational impact of CVE-2017-6738 extends significantly beyond simple system disruption, as successful exploitation can lead to complete system compromise and persistent access to network infrastructure. The vulnerability affects devices that have SNMP enabled, regardless of whether specific MIBs or OIDs are explicitly configured, meaning that any device with SNMP functionality active presents a potential target. Attackers leveraging this vulnerability can achieve unauthorized code execution with the privileges of the affected system, potentially enabling them to escalate their access to other network resources or establish persistent backdoors. The requirement for authentication adds a layer of complexity to exploitation but does not eliminate the risk, as SNMP community strings are often weak or default configurations that can be easily discovered through network reconnaissance. The system reload capability provides an additional attack vector that can be used for denial-of-service attacks, disrupting network management and operational continuity. This vulnerability directly maps to ATT&CK technique T1078 for valid accounts and T1059 for command and scripting interpreter, as attackers can leverage legitimate SNMP access to execute malicious commands and maintain persistence. The impact is particularly severe for network infrastructure devices, as compromise of these systems can provide attackers with visibility into entire network segments and enable further lateral movement attacks.
Mitigation strategies for CVE-2017-6738 must address both immediate defensive measures and long-term architectural improvements to protect against SNMP-based attacks. The most effective immediate mitigation involves disabling SNMP on devices where it is not strictly required, as this eliminates the attack surface entirely. For devices that must maintain SNMP functionality, implementing strict access controls through SNMP community string management and limiting access to trusted IP addresses provides essential protection. Network segmentation should be employed to isolate SNMP-enabled devices from critical network segments, reducing the potential impact of successful exploitation. The implementation of SNMPv3 with strong authentication and encryption mechanisms provides additional protection against credential-based attacks, as it eliminates the need for clear-text community strings that are required for v1 and v2c exploitation. Regular security audits should verify that SNMP configurations follow security best practices, including the use of strong passwords, disabling unnecessary MIBs, and implementing proper access controls. Network monitoring systems should be configured to detect anomalous SNMP traffic patterns that might indicate exploitation attempts, including unusual packet sizes or frequency of SNMP requests. Device firmware updates to the latest Cisco IOS releases containing patches for this vulnerability are essential, as they address the underlying buffer overflow conditions. The remediation process should also include disabling SNMPv1 and v2c where possible, as these versions are inherently less secure and more vulnerable to exploitation than the newer SNMPv3 protocol. Security teams should implement continuous monitoring for any signs of unauthorized SNMP access attempts and maintain detailed logs of SNMP activity for forensic analysis. The vulnerability demonstrates the importance of proper input validation in network services and highlights the need for regular security assessments of all network management protocols to prevent similar buffer overflow conditions from being exploited in the future.