CVE-2022-20854 Overview
A vulnerability exists in the processing of SSH connections within Cisco Firepower Management Center (FMC) and Cisco Firepower Threat Defense (FTD) Software that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on affected devices. This vulnerability is due to improper error handling when an SSH session fails to be established. An attacker could exploit this vulnerability by sending a high rate of crafted SSH connections to the instance, leading to resource exhaustion and forcing a device reboot.
Critical Impact
Successful exploitation allows unauthenticated attackers to remotely cause device reboots through SSH connection flooding, potentially disrupting network security monitoring and threat defense capabilities across enterprise environments.
Affected Products
- Cisco Secure Firewall Management Center versions 6.2.1 through 7.0.4
- Cisco Firepower Threat Defense versions 6.2.1 through 7.0.4
- Multiple point releases including 6.6.x and 7.0.x series
Discovery Timeline
- November 15, 2022 - CVE-2022-20854 published to NVD
- November 26, 2024 - Last updated in NVD database
Technical Details for CVE-2022-20854
Vulnerability Analysis
This denial of service vulnerability affects the SSH connection handling mechanism in both Cisco Firepower Management Center and Firepower Threat Defense software. The weakness stems from two underlying issues: improper handling of exceptional conditions (CWE-755) and uncontrolled resource consumption (CWE-400). When SSH sessions fail to establish properly, the software does not adequately handle the error condition, allowing resources to accumulate without proper cleanup.
The network-accessible nature of this vulnerability means that any attacker with network connectivity to the SSH service can attempt exploitation without requiring authentication or user interaction. The attack complexity is low, making it relatively straightforward for adversaries to execute. While confidentiality and integrity remain unaffected, the availability impact is significant as successful exploitation results in complete device unavailability through forced reboots.
Root Cause
The root cause of CVE-2022-20854 lies in improper error handling within the SSH session establishment process. When SSH connections fail during the handshake or authentication phase, the software fails to properly release allocated resources. This deficiency allows an attacker to rapidly accumulate system resources by initiating numerous SSH connection attempts that deliberately fail, ultimately exhausting available memory or connection handling capacity.
The combination of CWE-755 (Improper Handling of Exceptional Conditions) and CWE-400 (Uncontrolled Resource Consumption) indicates that the code path handling SSH failures does not include adequate cleanup routines or rate-limiting mechanisms to prevent resource accumulation from repeated failed connection attempts.
Attack Vector
The attack vector is network-based, allowing remote exploitation without authentication. An attacker can exploit this vulnerability by:
- Identifying a target Cisco FMC or FTD device with SSH services exposed
- Initiating a high rate of SSH connection attempts designed to fail during establishment
- Continuing the connection flood to exhaust system resources
- Triggering a device reboot once resource exhaustion thresholds are exceeded
The vulnerability does not require any special privileges, user interaction, or valid credentials. The attacker simply needs network access to the SSH port (typically TCP port 22) on the affected device. Organizations exposing management interfaces to untrusted networks are at elevated risk.
Detection Methods for CVE-2022-20854
Indicators of Compromise
- Unusual spike in SSH connection attempts from single or multiple source IP addresses
- High volume of failed SSH authentication or connection establishment events in system logs
- Unexpected device reboots or service restarts on FMC or FTD appliances
- Resource exhaustion warnings or memory pressure alerts on affected devices
- Network monitoring showing abnormal traffic patterns to SSH ports on firewall management systems
Detection Strategies
- Implement network-based intrusion detection rules to identify SSH connection flooding patterns targeting management interfaces
- Configure SIEM correlation rules to alert on excessive failed SSH connection attempts within short time windows
- Monitor system resource utilization (memory, CPU, connection tables) on FMC and FTD devices for anomalous consumption patterns
- Deploy behavioral analytics to detect deviation from baseline SSH connection patterns
Monitoring Recommendations
- Enable detailed SSH logging on affected devices to capture connection attempt metadata including source addresses and failure reasons
- Implement centralized log collection from all FMC and FTD devices to facilitate correlation and trend analysis
- Configure threshold-based alerts for SSH connection rates exceeding normal operational parameters
- Establish baseline metrics for device resource utilization to enable rapid detection of resource exhaustion attacks
How to Mitigate CVE-2022-20854
Immediate Actions Required
- Review the Cisco Security Advisory for specific remediation guidance and fixed software versions
- Restrict SSH access to management interfaces from trusted networks only using access control lists
- Implement rate limiting for SSH connections at network perimeter devices where possible
- Monitor affected devices for signs of exploitation while planning upgrade activities
Patch Information
Cisco has released security updates to address this vulnerability. Organizations should upgrade to fixed versions as specified in the Cisco Security Advisory. Affected version ranges include Cisco Secure Firewall Management Center and Firepower Threat Defense versions 6.2.1 through 7.0.4, including the 6.6.x series (6.6.0, 6.6.0.1, 6.6.1, 6.6.3, 6.6.4, 6.6.5, 6.6.5.1, 6.6.5.2) and 7.0.x series (7.0.0, 7.0.0.1, 7.0.1, 7.0.1.1, 7.0.2, 7.0.2.1, 7.0.3, 7.0.4).
Consult the official Cisco Security Advisory for specific fixed version numbers and upgrade paths applicable to your deployment.
Workarounds
- Restrict SSH access to management interfaces using access control lists (ACLs) to limit connections to trusted administrative IP addresses only
- Implement connection rate limiting on network devices in front of FMC and FTD appliances to throttle incoming SSH connection attempts
- Consider disabling SSH access on management interfaces and using alternative secure access methods such as console connections or out-of-band management networks
- Deploy network-based DoS protection mechanisms to detect and mitigate SSH flooding attacks before they reach affected devices
# Example ACL configuration to restrict SSH access on network device
# Replace 10.0.0.0/24 with your trusted management network
access-list 100 permit tcp 10.0.0.0 0.0.0.255 any eq 22
access-list 100 deny tcp any any eq 22
access-list 100 permit ip any any
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
