CVE-2022-20927: Cisco ASA Software DoS Vulnerability

CVE-2022-20927 Overview

A vulnerability in the SSL/TLS client of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper memory management when a device initiates SSL/TLS connections. An attacker could exploit this vulnerability by ensuring that the device will connect to an SSL/TLS server that is using specific encryption parameters. A successful exploit could allow the attacker to cause the affected device to unexpectedly reload, resulting in a DoS condition.

Critical Impact

Successful exploitation causes the affected Cisco ASA or FTD device to unexpectedly reload, disrupting network security services and potentially leaving protected networks exposed during the outage period.

Affected Products

• Cisco Adaptive Security Appliance (ASA) Software versions 9.13.x, 9.14.x, and 9.15.x
• Cisco Firepower Threat Defense (FTD) Software versions 6.6.x
• Cisco Firepower Services Software for ASA

Discovery Timeline

• November 15, 2022 - CVE-2022-20927 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-20927

Vulnerability Analysis

This denial of service vulnerability exists in the SSL/TLS client implementation of Cisco ASA and FTD software. The core issue lies in how these devices manage memory during SSL/TLS connection establishment. When an affected device initiates an outbound SSL/TLS connection to a server configured with specific encryption parameters, the improper memory management leads to memory corruption that triggers an unexpected device reload.

The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input), indicating that the memory corruption stems from insufficient bounds checking during SSL/TLS handshake processing. This is particularly concerning for network security appliances that serve as critical infrastructure components, as their unexpected reload creates a window where traffic may go unprotected or network connectivity is disrupted.

Root Cause

The root cause of CVE-2022-20927 is improper memory management within the SSL/TLS client component of the affected Cisco software. Specifically, when the device initiates SSL/TLS connections to servers using particular encryption parameters, the software fails to properly allocate or manage memory buffers during the cryptographic handshake process. This leads to a buffer overflow condition (CWE-120) that corrupts critical memory structures, ultimately causing the device to crash and reload.

Attack Vector

The attack requires an authenticated remote attacker who can influence the target device to establish an SSL/TLS connection to a malicious or compromised server. The attack vector involves:

1. The attacker sets up or compromises an SSL/TLS server with specific encryption parameters designed to trigger the vulnerability
2. The attacker must have authenticated access to the Cisco device or find a way to cause the device to initiate an outbound SSL/TLS connection to the attacker-controlled server
3. When the vulnerable device connects to the malicious server and processes the specially crafted encryption parameters, the memory corruption occurs
4. The device unexpectedly reloads, causing a denial of service condition

This vulnerability requires low attack complexity and can be exploited over the network, though it does require the attacker to have low-level privileges on the target device. The attack primarily affects availability with no impact on confidentiality or integrity.

Detection Methods for CVE-2022-20927

Indicators of Compromise

• Unexpected device reloads or crash logs referencing SSL/TLS client processing or memory allocation failures
• Crash dump files showing memory corruption in SSL/TLS-related processes
• Syslog messages indicating SSL/TLS handshake failures immediately before device reload events
• Patterns of outbound SSL/TLS connections to unfamiliar or suspicious external servers

Detection Strategies

• Monitor device crashinfo and show tech-support output for SSL/TLS-related crash signatures
• Implement network monitoring to detect unusual outbound SSL/TLS connection patterns from ASA/FTD devices
• Configure SNMP traps for device reload events and correlate with SSL/TLS connection logs
• Review connection logs for any outbound connections to unexpected or unauthorized SSL/TLS servers

Monitoring Recommendations

• Enable comprehensive logging for SSL/TLS client connections on affected devices
• Set up alerting for device availability using SNMP or Cisco-specific monitoring tools
• Monitor memory utilization patterns that may indicate abnormal behavior before crashes
• Implement network flow monitoring to baseline and detect anomalous outbound connection behavior

How to Mitigate CVE-2022-20927

Immediate Actions Required

• Review the Cisco Security Advisory to determine if your specific version is affected
• Plan and schedule software upgrades to patched versions during maintenance windows
• Audit configurations to identify features that cause the device to initiate outbound SSL/TLS connections
• Implement network segmentation to limit the servers that ASA/FTD devices can establish outbound connections to

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the official Cisco Security Advisory for detailed information on fixed software releases for their specific product version. The advisory provides guidance on determining the appropriate upgrade path based on the current software version and train.

For Cisco ASA Software, upgrade to a fixed release within the 9.13.x, 9.14.x, or 9.15.x trains as specified in the advisory. For Cisco FTD Software, upgrade to a fixed release within the 6.6.x train or migrate to a supported release train that includes the fix.

Workarounds

• Restrict outbound SSL/TLS connections from ASA/FTD devices to only trusted, known-good servers using access control lists
• Where possible, disable or limit features that initiate outbound SSL/TLS client connections until patching is complete
• Implement high availability configurations to minimize service disruption if a device reload occurs
• Monitor and filter outbound connections at upstream network devices to prevent connections to potentially malicious servers

# Example: Restrict outbound connections to specific trusted servers
# (Consult Cisco documentation for your specific deployment)
access-list OUTBOUND_SSL permit tcp host [ASA_IP] host [TRUSTED_SERVER] eq 443
access-list OUTBOUND_SSL deny tcp any any eq 443
access-group OUTBOUND_SSL out interface outside