SNMP Remote Code Execution Vulnerabilities in Cisco IOS and IOS XE Software

🚨 SEVERITY: HIGH — CVSS 8.8 Security Advisory

TL;DR 📌

  • The Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and IOS XE Software 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…
  • No fixed release listed yet; apply mitigations and monitor.
  • Workarounds are documented in the advisory.
  • CVEs: CVE-2017-6742, CVE-2017-6741, CVE-2017-6739.

What happened 🕵️‍♂️

The Simple Network Management Protocol (SNMP) is an application-layer protocol that provides a standardized framework and a common language for monitoring and managing devices in a network. It defines a message format for communication between SNMP managers and agents.

An SNMP agent gathers data from the SNMP MIB, which is the repository of information about device parameters and network data. It also responds to requests from an SNMP manager to get or set data. An SNMP agent contains MIB variables whose values can be requested or changed by an SNMP manager via get or set operations.

These vulnerabilities affect all versions of SNMP���Versions 1, 2c, and 3. An attacker could exploit these vulnerabilities by sending a crafted SNMP packet to an affected device via IPv4 or IPv6. Only traffic directed to the affected system can be used to exploit these vulnerabilities.

To exploit these vulnerabilities via SNMP Version 2c or earlier, the attacker must know the SNMP read-only community string for the affected system. A community string is a password that is applied to a device to restrict both read-only and read-write access to the SNMP data on the device. These community strings, as with all passwords, should be chosen carefully to ensure they are not trivial. They should also be changed at regular intervals and in accordance with network security policies. For example, the strings should be changed when a network administrator changes roles or leaves the organization.

To exploit these vulnerabilities via SNMP Version 3, the attacker must have user credentials for the affected system.

Affected products 🖥️

These vulnerabilities affect Cisco devices that are running a vulnerable release of Cisco IOS Software or Cisco IOS XE Software. These vulnerabilities affect all versions of SNMP, versions 1, 2c, and 3.

For information about which Cisco software releases are vulnerable, see the Fixed Software ["#fs"] section of this advisory.

Devices configured with any of the following MIBs are vulnerable:

ADSL-LINE-MIB ALPS-MIB CISCO-ADSL-DMT-LINE-MIB CISCO-AUTH-FRAMEWORK-MIB CISCO-BSTUN-MIB CISCO-MAC-AUTH-BYPASS-MIB CISCO-SLB-EXT-MIB CISCO-VOICE-DNIS-MIB CISCO-VOICE-NUMBER-EXPANSION-MIB TN3270E-RT-MIB

All of the MIBs listed above are enabled by default when SNMP is enabled. Some of the MIBs may not be present on all systems or versions but are enabled when present.

Administrators may be accustomed to utilizing the show snmp mib command in privileged EXEC mode to display a list of enabled MIBs on a device. Not all of the MIBs will be displayed in the output of the show snmp mib command but may still be enabled. Customers are advised to implement the entire exclude list as detailed in the Workarounds section of the advisory. Determining the Cisco IOS Software Release To determine which Cisco IOS Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS Software, the system banner displays text similar to Cisco Internetwork Operating System Software or Cisco IOS Software. The banner also displays the installed image name in parentheses, followed by the Cisco IOS Software release number and release name. Some Cisco devices do not support the show version command or may provide different output.

The following example identifies a Cisco product that is running Cisco IOS Software Release 15.5(2)T1 with an installed image name of C2951-UNIVERSALK9-M:

Router> show version

Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2015 by Cisco Systems, Inc. Compiled Mon 22-Jun-15 09:32 by prod_rel_team . . .

For information about the naming and numbering conventions for Cisco IOS Software releases, see White Paper: Cisco IOS and NX-OS Software Reference Guide [“http://www.cisco.com/web/about/security/intelligence/ios-ref.html”]. Determining the Cisco IOS XE Software Release To determine which Cisco IOS XE Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS XE Software, the system banner displays Cisco IOS XE Software or similar text.

The following example shows the output of the show version command on a device that is running Cisco IOS XE Software Release 3.16.1aS:

Router> show version

Cisco IOS XE Software, Version 03.16.01a.S - Extended Support Release Cisco IOS Software, ASR1000 Software (PPC_LINUX_IOSD-ADVENTERPRISEK9-M), Version 15.5(3)S1a, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2015 by Cisco Systems, Inc. Compiled Wed 04-Nov-15 17:40 by mcpre . . .

For information about the naming and numbering conventions for Cisco IOS XE Software releases, see White Paper: Cisco IOS and NX-OS Software Reference Guide [“http://www.cisco.com/c/en/us/about/security-center/ios-nx-os-reference-guide.html”].

Fixed software 🔧

Upgrade to the first fixed release in your train (or later):

Release / Product First Fixed Release Notes
1.11 Added an additional MIB to filter in the workarounds.
1.10 Updated to further clarify that these vulnerabilities only impact software prior to first fixed releases.
1.9 Updated to clarify vulnerable products.
1.8 Updated the Exploitation and Public Announcements section to clarify CVEs targeted by public exploitation.
1.7 Updated the Exploitation and Public Announcements section with information on public exploitation.
1.6 Added information about public exploit availability.
1.5 Re-added Cisco Bug ID CSCve60507 to bug list.
1.4 Indicated that fixed software is available. Added links to the Cisco IOS Software Checker.
1.3 Added OVAL definitions.
1.2 Added statement regarding fixed software and workarounds to the Summary section. Removed information regarding the Cisco IOS Software Checker. The tool is currently experiencing issues and returning inconsistent results to customer queries.
1.1 Added Statement to Vulnerable Products to indicate that all affected MIBs are enabled by default on affected versions and hardware configurations if SNMP is enabled. Updated information in Vulnerable Products to indicate that the ‘show snmp mib’ command was insufficient to determine if a device is affected. Added comments to the Workaround configuration commands to document which exclusions tie to the vulnerable MIBs.
1.0 Initial public release.

Workarounds 🧯

Administrators are advised to allow only trusted users to have SNMP access on an affected system. Administrators are also advised to monitor affected systems by using the show snmp host command in the CLI.

In addition, administrators can mitigate these vulnerabilities by disabling the following MIBs on a device:

ADSL-LINE-MIB ALPS-MIB CISCO-ADSL-DMT-LINE-MIB CISCO-AUTH-FRAMEWORK-MIB CISCO-BSTUN-MIB CISCO-MAC-AUTH-BYPASS-MIB CISCO-SLB-EXT-MIB CISCO-VOICE-DNIS-MIB CISCO-VOICE-NUMBER-EXPANSION-MIB TN3270E-RT-MIB

To create or update a view entry and disable the affected MIBs, administrators can use the snmp-server view global configuration command, as shown in the following example:

!Standard VIEW and Security Exclusions snmp-server view NO_BAD_SNMP iso included snmp-server view NO_BAD_SNMP internet included snmp-server view NO_BAD_SNMP snmpUsmMIB excluded snmp-server view NO_BAD_SNMP snmpVacmMIB excluded snmp-server view NO_BAD_SNMP snmpCommunityMIB excluded snmp-server view NO_BAD_SNMP ciscoMgmt.252 excluded !End Standard View

!Advisory Specific Mappings !ADSL-LINE-MIB snmp-server view NO_BAD_SNMP transmission.94 excluded

!TN3270E-RT-MIB snmp-server view NO_BAD_SNMP mib-2.34.9 excluded

!CISCO-BSTUN-MIB snmp-server view NO_BAD_SNMP ciscoMgmt.35 excluded

!ALPS-MIB snmp-server view NO_BAD_SNMP ciscoMgmt.95 excluded

!CISCO-ADSL-DMT-LINE-MIB snmp-server view NO_BAD_SNMP ciscoMgmt.130 excluded

!CISCO-AUTH-FRAMEWORK-MIB snmp-server view NO_BAD_SNMP ciscoAuthFrameworkMIB excluded

!CISCO-VOICE-DNIS-MIB snmp-server view NO_BAD_SNMP ciscoMgmt.219 excluded

!CISCO-SLB-EXT-MIB snmp-server view NO_BAD_SNMP ciscoMgmt.254 excluded

!CISCO-MAC-AUTH-BYPASS-MIB snmp-server view NO_BAD_SNMP ciscoMabMIB excluded

!CISCO-VOICE-NUMBER-EXPANSION-MIB snmp-server view NO_BAD_SNMP ciscoExperiment.997 excluded

To then apply this configuration to a community string, administrators can use the following command:

snmp-server community mycomm view NO_BAD_SNMP RO

For SNMP Version 3, administrators can use the following command:

snmp-server group v3group auth read NO_BAD_SNMP write NO_BAD_SNMP

Risk in context 🎯

Use vendor CVSS for prioritization. Consider exposure and asset criticality.

Fast facts ⚡

  • Advisory: cisco-sa-20170629-snmp
  • Initial release: 2017-06-29T16:00:00 UTC
  • Last updated: 2025-07-30T16:27:06 UTC

For leadership 🧭

Executive summary. Risk is High (CVSS 8.8) for 12.0, 12.0(1). Vendor fixes are available; prioritize upgrade within 7 days based on environment risk.

Why it matters (exposure drivers):

  • Potential service impact and security exposure depend on deployment topology and access paths.
  • Treat internet-exposed or multi-tenant management nodes as higher risk.
  • Ensure monitoring for abnormal auth/config events until upgrades complete.

Remediation & timing:

  • Upgrade to the first fixed release per the table above; schedule an approved change window within 7 days.
  • Change risk: low-to-moderate (standard vendor patch). Validate backups and rollback plan.

Now / Next / Later:

  • Now: Confirm exposure, identify affected versions, and enable monitoring/alerts.
  • Next: Patch according to the fixed software table; verify service health post-change.
  • Later: Add control checks to build pipeline/CMDB to block drift to vulnerable trains.