CVE-2017-6742: Cisco IOS and IOS XE Software SNMP Remote Code Execution Vulnerability

CVE-2017-6742 is a remote code execution vulnerability in the Simple Network Management Protocol (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 a reload, disrupting network operations.

Because IOS and IOS XE power core routers and switches, successful exploitation can give an attacker a foothold deep inside the infrastructure. Confirm exact impact and affected releases against the vendor advisory.

How it works

The flaw is classified as CWE-119, an improper restriction of operations within the bounds of a memory buffer. In the SNMP subsystem this means crafted SNMP traffic can corrupt memory on the device.

An attacker who already possesses valid SNMP credentials (community string or SNMPv3 user) can send specially formed SNMP packets. The malformed input triggers the buffer issue, allowing the attacker either to run arbitrary code with the privileges of the SNMP process or to crash the device so that it reloads. No unauthenticated path is described; authentication is required. Exact packet structure and exploit mechanics are not public in the provided facts and must be verified in the vendor advisory.

Am I affected? How to find it in your systems

Cisco IOS and IOS XE typically run on enterprise and service-provider routers, switches, and some wireless controllers. Inventory every device that speaks SNMP.

• Collect the full software version string from each device (show version or equivalent).
• Compare that string against the fixed releases listed in the Cisco advisory for CVE-2017-6742; do not rely on version ranges published elsewhere.
• Confirm whether SNMP is enabled and which community strings or SNMPv3 users are configured.
• Review SNMP access-control lists and source-address restrictions; unrestricted SNMP from untrusted networks increases exposure.

Telemetry signs of attempted exploitation include unexpected SNMP authentication failures, sudden device reloads, or anomalous high-rate SNMP traffic from a single source. Correlate these events with authentication logs and configuration change records. Because public detail on specific indicators is limited, treat any unexplained SNMP-related crash as suspicious until investigated.

How to remediate

Apply the software updates published by Cisco for this vulnerability. The CISA-required action is simply “Apply updates per vendor instructions.” Download the fixed image from the official Cisco channel, stage it, and reload the device during a maintenance window after verifying the image integrity.

After patching:

• Disable SNMP if it is not operationally required.
• If SNMP must remain, migrate to SNMPv3 with strong authentication and encryption; remove all SNMPv1/v2c community strings.
• Restrict SNMP access with interface ACLs or control-plane policing so that only management stations can reach the service.
• Rotate any community strings or SNMPv3 credentials that may have been exposed.

These steps reduce the attack surface for the entire SNMP subsystem, not only this CVE.

If you can't patch immediately

Until the vendor update can be installed, apply compensating controls that limit reachability and privilege:

• Segment management interfaces onto a dedicated out-of-band network unreachable from user or guest VLANs.
• Deploy infrastructure ACLs or firewall rules that permit SNMP only from known management stations and drop all other SNMP traffic.
• If a web application firewall or IPS is in the path, enable any available SNMP protocol anomaly signatures; treat this as temporary virtual patching only.
• Disable the SNMP server entirely on devices that do not require it for monitoring.
• Increase logging of SNMP authentication events and device reloads; forward them to a central SIEM for real-time alerting.

These measures shrink the window of opportunity but do not eliminate the underlying memory-corruption risk; schedule the official patch as soon as possible.

If your data may have been exposed

Actively exploited remote-code-execution flaws on network devices can lead to full compromise of the device and subsequent lateral movement or data exfiltration. Known ransomware use of this specific CVE is not documented. If you suspect exploitation, isolate the affected device, preserve logs and memory if possible, and begin incident-response procedures. As a quick additional check, you can run a free exposure scan of your email addresses against known breach data sets to see whether any associated credentials have already appeared in public dumps.