CVE-2020-3217: Cisco IOS onePK RCE Vulnerability

CVE-2020-3217 Overview

A vulnerability in the Topology Discovery Service of Cisco One Platform Kit (onePK) in Cisco IOS Software, Cisco IOS XE Software, Cisco IOS XR Software, and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to execute arbitrary code or cause a denial of service (DoS) condition on an affected device. The vulnerability is due to insufficient length restrictions when the onePK Topology Discovery Service parses Cisco Discovery Protocol messages. An attacker could exploit this vulnerability by sending a malicious Cisco Discovery Protocol message to an affected device. An exploit could allow the attacker to cause a stack overflow, which could allow the attacker to execute arbitrary code with administrative privileges, or to cause a process crash, which could result in a reload of the device and cause a DoS condition.

Critical Impact

Successful exploitation allows unauthenticated adjacent attackers to achieve arbitrary code execution with administrative privileges or cause device reload, potentially disrupting critical network infrastructure.

Affected Products

• Cisco IOS Software (multiple versions including 12.2, 15.x series)
• Cisco IOS XE Software (versions 3.7.x through 16.12.x)
• Cisco IOS XR Software (all versions)
• Cisco NX-OS Software (versions 6.0, 6.1, 7.x, 8.x series)
• Cisco Nexus 3000, 5000, 6000, and 7000 Series Switches

Discovery Timeline

• June 3, 2020 - CVE-2020-3217 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-3217

Vulnerability Analysis

This vulnerability affects the Topology Discovery Service component within Cisco's One Platform Kit (onePK), a framework that enables programmatic access to Cisco network devices. The vulnerability stems from improper input validation when processing Cisco Discovery Protocol (CDP) messages, a Layer 2 protocol used for device discovery in Cisco environments.

The onePK Topology Discovery Service fails to properly enforce length restrictions when parsing incoming CDP messages. When a specially crafted CDP message containing excessive data is received, the service attempts to copy this data into a fixed-size stack buffer without adequate bounds checking. This results in a classic stack buffer overflow condition where attacker-controlled data overwrites adjacent stack memory, including return addresses and saved registers.

The exploitation requires Layer 2 adjacency, meaning an attacker must be on the same network segment as the target device or be able to inject frames at Layer 2. Once exploited, the attacker can achieve arbitrary code execution with administrative (root) privileges on the affected device, providing complete control over the network infrastructure. Alternatively, the overflow may cause the onePK process to crash, triggering a device reload and resulting in denial of service.

Root Cause

The root cause is insufficient input validation (CWE-20) in the onePK Topology Discovery Service when parsing Cisco Discovery Protocol messages. The service fails to validate the length of data fields within CDP packets before copying them into stack-allocated buffers. This allows an attacker to supply oversized data that exceeds the buffer boundaries, resulting in a stack overflow condition. The lack of proper bounds checking during the parsing operation creates a directly exploitable memory corruption vulnerability.

Attack Vector

The attack requires an adjacent network position (Layer 2 connectivity) to the target device. An attacker must be able to send Cisco Discovery Protocol frames to an interface where CDP is enabled and the onePK Topology Discovery Service is running. The attack can be executed without authentication since CDP operates at Layer 2 and the vulnerable service processes incoming messages without credential verification.

The attacker crafts a malicious CDP frame with manipulated length fields and payload data designed to overflow the stack buffer. When the vulnerable service processes this frame, the overflow corrupts stack memory. With careful construction of the payload, the attacker can overwrite the return address to redirect execution flow to attacker-controlled code, achieving remote code execution with full administrative privileges.

Detection Methods for CVE-2020-3217

Indicators of Compromise

• Unexpected device reloads or crashes with core dumps referencing onePK or CDP processing functions
• Abnormal CDP traffic patterns including malformed or oversized CDP frames on network segments
• Unusual process behavior or memory consumption associated with onePK services
• Syslog entries indicating CDP parsing errors or memory corruption events

Detection Strategies

• Deploy network intrusion detection systems (IDS) with signatures for malformed CDP frames and anomalous Layer 2 traffic
• Monitor device logs for unexpected crashes, core dumps, or process restarts related to onePK services
• Implement CDP packet inspection at network boundaries where feasible to identify oversized or malformed messages
• Enable device-level crash analysis and memory dump collection for forensic investigation

Monitoring Recommendations

• Configure SNMP traps for device reload events and process crashes on affected Cisco devices
• Establish baseline CDP traffic patterns and alert on significant deviations indicating potential exploitation attempts
• Implement centralized logging for all Cisco infrastructure devices with real-time alerting on relevant error conditions
• Monitor for unauthorized Layer 2 access or rogue devices that could serve as attack launch points

How to Mitigate CVE-2020-3217

Immediate Actions Required

• Apply the appropriate security patches from Cisco immediately for all affected IOS, IOS XE, IOS XR, and NX-OS devices
• Disable Cisco Discovery Protocol (CDP) on interfaces where it is not required for network operations
• Disable the onePK feature if it is not actively used in your environment
• Restrict Layer 2 network access through port security, 802.1X authentication, and network segmentation

Patch Information

Cisco has released software updates addressing this vulnerability. Administrators should consult the Cisco Security Advisory for the specific fixed software versions applicable to their deployment. The advisory provides detailed information on affected versions and corresponding patches for IOS, IOS XE, IOS XR, and NX-OS platforms.

Workarounds

• Disable CDP globally or on specific interfaces where neighbor discovery is not required using the no cdp enable interface command or no cdp run global command
• Disable the onePK feature if not in use with no onep or equivalent configuration commands
• Implement strict Layer 2 access controls including port security, MAC address filtering, and 802.1X authentication to limit adjacent network access
• Segment network infrastructure devices onto dedicated management VLANs with restricted access

# Disable CDP globally on Cisco IOS/IOS XE devices
configure terminal
no cdp run
exit

# Alternatively, disable CDP on specific interfaces
configure terminal
interface GigabitEthernet0/0
 no cdp enable
exit