CVE-2022-20685: Cisco Cyber Vision DoS Vulnerability

CVE-2022-20685 Overview

CVE-2022-20685 is an integer overflow vulnerability in the Modbus preprocessor of the Snort detection engine that allows an unauthenticated, remote attacker to cause a denial of service (DoS) condition on affected devices. The vulnerability exists due to improper handling of integer values while processing Modbus traffic, which can cause the Snort process to hang and stop traffic inspection entirely.

This vulnerability is particularly concerning for industrial control system (ICS) environments where Modbus protocol is commonly used for SCADA communications. When exploited, the Snort intrusion detection and prevention system becomes unresponsive, leaving the network without critical security monitoring and inspection capabilities.

Critical Impact

Successful exploitation causes the Snort process to hang, completely halting traffic inspection and leaving networks unprotected against intrusion attempts.

Affected Products

• Cisco Cyber Vision (versions 3.0.0 through 4.0.1)
• Cisco Firepower Threat Defense (versions 6.2.3 through 7.0.0.1)
• Cisco Unified Threat Defense Snort Intrusion Prevention System Engine (multiple versions including 16.x, 17.x series)

Discovery Timeline

• November 15, 2024 - CVE-2022-20685 published to NVD
• June 24, 2025 - Last updated in NVD database

Technical Details for CVE-2022-20685

Vulnerability Analysis

The vulnerability resides in the Modbus preprocessor component of the Snort detection engine, which is responsible for analyzing Modbus protocol traffic for potential security threats. The integer overflow condition occurs when the preprocessor processes specially crafted Modbus packets with malformed length or count fields.

When the Snort engine parses Modbus traffic, it uses integer values to calculate buffer sizes and loop iterations. By providing values that cause integer overflow, an attacker can trigger unexpected behavior in the processing logic. The integer overflow (CWE-190) results in the Snort process entering a hung state, effectively creating a denial of service condition.

The impact is severe for organizations relying on Snort-based intrusion detection, as the vulnerability can be exploited remotely without authentication, requiring only the ability to send crafted Modbus packets through a device running the vulnerable software.

Root Cause

The root cause is an integer overflow vulnerability (CWE-190) in the Modbus protocol preprocessor within Snort. When processing Modbus traffic, certain integer calculations do not properly validate input values before performing arithmetic operations. This allows an attacker to supply values that overflow the integer type, leading to incorrect buffer calculations or infinite loops that cause the process to hang.

Integer overflow occurs when an arithmetic operation produces a result larger than the maximum value that can be stored in the integer data type. In this case, the overflow causes the Snort preprocessor to enter an unexpected state where it cannot continue processing traffic.

Attack Vector

The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker needs to send specially crafted Modbus protocol traffic through a device running a vulnerable version of Snort. The attack methodology involves:

1. Identifying a target device running vulnerable Snort-based inspection (Cisco FTD, Cyber Vision, or UTD Snort IPS)
2. Crafting Modbus packets with specific field values designed to trigger the integer overflow condition
3. Sending the malicious Modbus traffic through the target device
4. The Snort preprocessor processes the crafted packets and enters a hung state

The attack does not require direct access to the target device—traffic only needs to pass through the inspection point. This makes the vulnerability particularly dangerous in environments where Modbus traffic traverses network security appliances.

Detection Methods for CVE-2022-20685

Indicators of Compromise

• Snort process becoming unresponsive or entering a hung state without apparent cause
• Traffic inspection stopping suddenly while the device appears otherwise functional
• Unusual Modbus traffic patterns with abnormally large length or count field values
• System logs showing Snort preprocessor errors or timeout events related to Modbus processing

Detection Strategies

• Monitor Snort process health and responsiveness using system watchdog mechanisms
• Implement network-level detection for malformed Modbus packets with suspicious integer values
• Deploy SentinelOne Singularity platform to detect anomalous process behavior and service disruptions
• Configure alerting for Snort service interruptions or unexpected restarts

Monitoring Recommendations

• Enable detailed logging for the Modbus preprocessor to capture parsing errors and anomalies
• Implement process monitoring to detect when Snort enters a non-responsive state
• Monitor network traffic for Modbus protocol anomalies, particularly packets with unusual PDU sizes
• Use SentinelOne's behavioral AI to identify denial of service attack patterns targeting security infrastructure

How to Mitigate CVE-2022-20685

Immediate Actions Required

• Review the Cisco Security Advisory for affected version details
• Identify all devices in your environment running vulnerable versions of Cisco FTD, Cyber Vision, or UTD Snort IPS
• Prioritize patching for devices that inspect Modbus/SCADA traffic in ICS environments
• Consider implementing network segmentation to limit exposure of vulnerable inspection points to untrusted traffic

Patch Information

Cisco has released software updates that address this vulnerability. Organizations should upgrade to the fixed versions as specified in the Cisco Security Advisory. According to Cisco, there are no workarounds that fully address this vulnerability, making patching the only complete remediation option.

For Cisco Firepower Threat Defense, upgrade to a fixed release beyond version 7.0.0.1. For Cisco Cyber Vision, upgrade beyond version 4.0.1. For UTD Snort IPS Engine, consult the advisory for specific fixed version information for your IOS-XE release.

Workarounds

• No official workarounds are available according to Cisco's advisory
• As a temporary measure, consider disabling the Modbus preprocessor if Modbus traffic inspection is not required for your environment
• Implement strict network access controls to limit which sources can send Modbus traffic through vulnerable devices
• Deploy additional monitoring to quickly detect and respond to service disruptions

# Verify current Snort version on Cisco FTD
show version

# Check Snort preprocessor status
show snort preprocessor-memory-usage

# Monitor Snort process health
show snort statistics