Cisco Catalyst 6800 Switches VPLS Memory Management Vulnerability (CVE-2017-12238) Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTCisco Catalyst 6800 Series Switches running Cisco IOS 15.0 through 15.4, equipped with Supervisor Engine 6T and C6800-16P10G or C6800-16P10G-XL line cards configured as core-facing MPLS interfaces with VPLS enabled.
An unauthenticated, adjacent attacker can flood the device with VPLS-generated MAC entries, causing the affected line card to crash and resulting in a complete Denial of Service (DoS) condition.
Upgrade to a fixed Cisco IOS software release addressing Cisco Bug ID CSCva61927, or implement MAC address learning limits on VPLS VFIs as a temporary workaround.
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Administrators should upgrade to a non-vulnerable Cisco IOS release that resolves Cisco Bug ID CSCva61927. Below is an example of upgrading the IOS image via TFTP:
# Copy the patched IOS image from TFTP server to flash
Switch# copy tftp: flash:
Address or name of remote host? 192.168.1.100
Source filename? c6800-adventerprisek9-mz.SPA.15.x-xxx.bin
Destination filename [c6800-adventerprisek9-mz.SPA.15.x-xxx.bin]?
# Configure the boot system path and reload
Switch# configure terminal
Switch(config)# no boot system
Switch(config)# boot system flash:c6800-adventerprisek9-mz.SPA.15.x-xxx.bin
Switch(config)# end
Switch# write memory
Switch# reload2. Temporary Workaround & Hardening Configuration
If an immediate upgrade is not feasible, limit the maximum number of MAC addresses that can be learned dynamically within the VPLS Virtual Forwarding Instance (VFI) to prevent resource exhaustion.
Switch# configure terminal
# Enter VPLS VFI configuration mode and apply MAC limit
Switch(config)# l2 vfi VPLS-WAN manual
Switch(config-vfi)# vpn id 100
Switch(config-vfi)# mac limit 1000 action limit
Switch(config-vfi)# end
Switch# write memory3. Log Audit & IoC Verification Commands
Verify the hardware configuration, VPLS status, and inspect system logs for any signs of line card instability or memory exhaustion.
# 1. Verify IOS version and line card model
show version | include IOS
show module | include C6800-16P10G
# 2. Check VPLS VFI status and MAC table size
show vfi
show mac address-table count
# 3. Inspect logs for line card crashes or memory allocation failures
show logging | include -3-CARD_CRASHED|SYS-3-LOGGER|MemoryStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2017-12238) exists in the Virtual Private LAN Service (VPLS) software code of Cisco IOS. The root cause is a memory management issue (CWE-399) within the affected software when running on Cisco Catalyst 6800 Series Switches configured with Supervisor Engine 6T and C6800-16P10G or C6800-16P10G-XL line cards. The system fails to properly manage memory resources when processing an excessive number of MAC address table entries generated via VPLS.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated attacker located on an adjacent Layer 2 network can exploit this vulnerability. By transmitting a high volume of crafted Ethernet frames with randomized source MAC addresses into the VPLS domain, the attacker forces the target switch to populate its MAC address table with a massive number of VPLS-generated MAC entries. This triggers a memory exhaustion state on the core-facing C6800-16P10G or C6800-16P10G-XL line card, leading to a kernel panic/crash of the line card.
3. Infrastructure & Business Impact
As a CISA KEV-listed vulnerability, this flaw poses a severe threat to enterprise and service provider core networks. A crash of the core-facing MPLS line card disrupts all transit traffic passing through the affected switch. This can lead to widespread network outages, loss of connectivity for downstream sites, and significant disruption to business-critical operations.
Official Vendor Advisories & References
A vulnerability in the Virtual Private LAN Service (VPLS) code of Cisco IOS 15.0 through 15.4 for Cisco Catalyst 6800 Series Switches could allow an unauthenticated, adjacent attacker to cause a C6800-16P10G or C6800-16P10G-XL type line card to crash, resulting in a denial of service (DoS) condition. The vulnerability is due to a memory management issue in the affected software. An attacker could exploit this vulnerability by creating a large number of VPLS-generated MAC entries in the MAC address table of an affected device. A successful exploit could allow the attacker to cause a C6800-16P10G or C6800-16P10G-XL type line card to crash, resulting in a DoS condition. This vulnerability affects Cisco Catalyst 6800 Series Switches that are running a vulnerable release of Cisco IOS Software and have a Cisco C6800-16P10G or C6800-16P10G-XL line card in use with Supervisor Engine 6T. To be vulnerable, the device must also be configured with VPLS and the C6800-16P10G or C6800-16P10G-XL line card needs to be the core-facing MPLS interfaces. Cisco Bug IDs: CSCva61927.
Frequently Asked SecOps Questions (CVE-2017-12238)
FAQQ1. How critical is CVE-2017-12238 and is it actively exploited in the wild?
CVE-2017-12238 is rated CVSS 6.5 (MEDIUM) with a 30-day EPSS exploitation probability of 2.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2017-12238?
Primary impacted vendors include cisco across catalyst_6800, ios. Scope summary: Cisco Catalyst 6800 Series Switches running Cisco IOS Software releases 15.0 through 15.4, utilizing Supervisor Engine 6T and C6800-16P10G / C6800-16P10G-XL line cards configured as core-facing MPLS interfaces with VPLS enabled.
Q3. What temporary mitigations or workarounds exist for CVE-2017-12238 before patching?
[Mitigation] Upgrade to a fixed Cisco IOS software release addressing Cisco Bug ID CSCva61927, or implement MAC address learning limits on VPLS VFIs as a temporary workaround. Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2017-12238
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
🔗 Related Advisories in Similar Stack (cisco)
View Category →Cisco Identity Services Engine (ISE) Critical Authentication Bypass Vulnerability (CVE-2026-76460)
[Affected Scope] Cisco Identity Services Engine (ISE) web-based management interface and API endpoints.
Cisco Catalyst SD-WAN Peering Authentication Bypass Vulnerability (CVE-2026-20182)
[Affected Scope] Cisco Catalyst SD-WAN Controller (formerly vSmart), Manager (formerly vManage), and Validator (formerly vBond)
Cisco Secure Firewall Management Center (FMC) Insecure Deserialization Vulnerability (CVE-2026-20131, CVSS 10.0) - Remote Code Execution and Root Privilege Escalation
[Affected Scope] Web-based management interface of Cisco Secure Firewall Management Center (FMC) Software.
Cisco Secure Firewall Management Center (FMC) Authentication Bypass and Root RCE Vulnerability (CVE-2026-20079)
[Affected Scope] Web-based management interface of Cisco Secure Firewall Management Center (FMC) Software
Subscribe to Daily Vulnerability Briefings & KEV Alerts
Concise morning briefings for SecOps, DevSecOps, and SRE teams covering newly exploited CVEs and mitigation priorities.