CVE-2017-6740: Cisco IOS and IOS XE Software SNMP Remote Code Execution Vulnerability

CVE-2017-6740 is a vulnerability in the SNMP subsystem of Cisco IOS and IOS XE Software. An authenticated remote attacker could use it to execute code on an affected device or force the device to reload. Network infrastructure that relies on these platforms for routing, switching, or other core functions is therefore at risk if SNMP is enabled and reachable by an attacker who can authenticate.

Because the flaw sits in a widely used management protocol on enterprise and service-provider gear, successful abuse can disrupt operations or give an attacker a foothold deeper in the network. Confirm exact affected releases and fixed software against the vendor advisory.

How it works

The weakness is classified as CWE-119 (improper restriction of operations within the bounds of a memory buffer). In the SNMP subsystem of Cisco IOS and IOS XE, crafted input that reaches the vulnerable code path can corrupt memory. An attacker who can authenticate to SNMP and send specially formed SNMP traffic may trigger that corruption.

Depending on how the memory is corrupted, the result can be remote code execution with the privileges of the affected process or a device reload that causes denial of service. Public detail on precise packet formats or exploit mechanics is limited; treat any proof-of-concept material with caution and validate behavior only in controlled lab conditions against the vendor’s description.

Am I affected? How to find it in your systems

Cisco IOS and IOS XE commonly run on routers, switches, wireless controllers, and other network devices. Inventory every device that speaks SNMP and is running IOS or IOS XE.

• Collect software version strings (show version or equivalent inventory tools) and compare them with the fixed releases listed in the Cisco advisory for CVE-2017-6740.
• Identify whether SNMP is enabled, which versions (v1/v2c/v3) are in use, and which community strings or SNMPv3 credentials are configured.
• Note management-plane ACLs, VRF isolation, and whether SNMP is exposed only to trusted management hosts or is reachable from broader networks.
• Review logs and telemetry for unexpected SNMP authentication successes from unfamiliar sources, device reloads coincident with SNMP activity, or anomalous SNMP PDU patterns. Absence of such signs does not prove the device is clean; it only indicates no obvious exploitation was recorded.

Exact version ranges and configuration prerequisites must be confirmed against the vendor advisory; do not rely on third-party summaries alone.

How to remediate

Patch first. Apply the Cisco software updates that address CVE-2017-6740 exactly as directed in the vendor advisory and CISA’s required action to apply updates per vendor instructions.

• Schedule maintenance windows for devices that cannot be upgraded in-service; verify the target image is the correct fixed release for your hardware and feature set.
• After upgrade, re-validate SNMP configuration, remove unused communities or weak SNMPv1/v2c credentials, and enforce SNMPv3 with strong authentication and encryption where SNMP remains necessary.
• Restrict SNMP access with interface or control-plane ACLs so only authorized management stations can reach the service.
• Disable SNMP entirely on devices that do not require it for operations or monitoring.

If you can't patch immediately

Reduce exposure until the vendor update can be installed:

• Segment management access: place device management interfaces in a dedicated network reachable only from jump hosts or management workstations.
• Apply or tighten infrastructure ACLs and control-plane policing to drop SNMP from untrusted sources.
• If a web application firewall or network IPS is in the path and offers signatures for this CVE or generic SNMP memory-corruption patterns, enable them as a temporary virtual patch; confirm coverage with the security vendor.
• Disable the SNMP service or unnecessary SNMP views/communities if operationally feasible.
• Increase monitoring for authentication anomalies, unexpected reloads, and configuration changes on unpatched devices, and alert on any SNMP traffic from outside the approved management set.

These steps only lower risk; they do not replace the software fix.

If your data may have been exposed

Actively exploited vulnerabilities on network devices can lead to broader compromise and data exposure. Known ransomware use of this CVE is not documented, but any successful code execution or persistent access should be treated as a potential incident. Investigate device integrity, review downstream systems that trust the affected gear, and rotate credentials that may have traversed the device. You can also run a free exposure scan of your email addresses to check whether they appear in known breach data sets.