CVE-2024-20330 Overview
A memory corruption vulnerability exists in the Snort 2 and Snort 3 TCP and UDP detection engine of Cisco Firepower Threat Defense (FTD) Software for Cisco Firepower 2100 Series Appliances. This vulnerability allows an unauthenticated, remote attacker to cause memory corruption, leading to unexpected restarts of the Snort detection engine and resulting in a denial of service (DoS) condition.
The vulnerability stems from improper memory management when the Snort detection engine processes specific TCP or UDP packets. An attacker can exploit this flaw by sending crafted TCP or UDP packets through a device that is inspecting traffic using the Snort detection engine. Successfully exploiting this vulnerability causes repeated Snort detection engine crashes, disrupting traffic inspection capabilities.
Critical Impact
Once memory corruption occurs, it cannot be cleared until the Cisco Firepower 2100 Series Appliance is manually reloaded. This means the Snort detection engine will continue crashing repeatedly, causing all traffic processed by Snort to be dropped until a manual device reload is performed.
Affected Products
- Cisco Firepower Threat Defense (FTD) Software versions 7.0.x through 7.4.2
- Cisco Firepower 2100 Series Appliances (2110, 2120, 2130, 2140)
- Systems running Snort 2 or Snort 3 detection engines
Discovery Timeline
- October 23, 2024 - CVE-2024-20330 published to NVD
- August 6, 2025 - Last updated in NVD database
Technical Details for CVE-2024-20330
Vulnerability Analysis
This vulnerability is classified under CWE-788 (Access of Memory Location After End of Buffer), indicating that the Snort detection engine improperly accesses memory beyond allocated buffer boundaries during TCP and UDP packet processing. The flaw resides specifically in how the detection engine handles memory allocation and deallocation when inspecting network traffic.
The vulnerability is particularly severe because it affects the core traffic inspection functionality of Cisco Firepower appliances. While the device remains manageable over the network even during exploitation, all traffic that passes through the Snort inspection engine is subject to disruption. The persistent nature of the memory corruption means that once triggered, the only recovery mechanism is a complete manual reload of the appliance.
Root Cause
The root cause of CVE-2024-20330 is improper memory management within the Snort detection engine when processing specific TCP or UDP packets. The detection engine fails to properly handle memory boundaries during packet inspection, leading to memory corruption when certain packet patterns are encountered. This corruption persists in memory blocks and cannot be automatically cleared by the system, requiring manual intervention to restore normal operation.
Attack Vector
The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker needs only the ability to send crafted TCP or UDP packets through a network path that is being inspected by a vulnerable Cisco Firepower 2100 Series Appliance running affected FTD software.
The attack flow involves:
- The attacker identifies a network path monitored by a vulnerable Firepower 2100 appliance
- Specially crafted TCP or UDP packets are sent through the device
- The Snort detection engine processes these packets, triggering memory corruption
- The corrupted memory causes the Snort engine to crash and restart
- Due to persistent memory corruption, subsequent traffic processing continues to trigger crashes
- Traffic inspection becomes unavailable until the device is manually reloaded
Detection Methods for CVE-2024-20330
Indicators of Compromise
- Repeated Snort detection engine restart events in system logs
- Unexpected traffic drops through the Firepower appliance without corresponding policy blocks
- High frequency of Snort process crash events in the Firepower Management Center
- Network traffic bypassing inspection due to engine unavailability
Detection Strategies
- Monitor Snort engine health status and restart frequency through Firepower Management Center
- Configure SNMP traps or syslog alerts for Snort detection engine failures
- Implement network traffic analysis to detect unusual patterns of inspected traffic interruptions
- Review system health dashboards for abnormal engine restart patterns
Monitoring Recommendations
- Enable detailed logging for Snort engine events on Firepower 2100 Series appliances
- Set up automated alerting for multiple Snort engine restarts within short time periods
- Correlate Snort crash events with incoming network traffic patterns to identify potential attack sources
- Monitor for degraded throughput or increased latency indicative of inspection failures
How to Mitigate CVE-2024-20330
Immediate Actions Required
- Review Cisco's security advisory and determine if your FTD software version is affected
- Schedule maintenance windows to apply patches to vulnerable Firepower 2100 Series appliances
- Consider implementing additional network controls to filter suspicious TCP/UDP traffic before reaching affected devices
- Establish procedures for rapid manual device reload if exploitation is suspected
Patch Information
Cisco has released security updates to address this vulnerability. Affected organizations should consult the Cisco Security Advisory for specific version guidance and upgrade paths. The following FTD software version ranges are known to be affected:
- FTD versions 7.0.0.0 through 7.0.6.3
- FTD versions 7.1.0 through 7.1.0.3
- FTD versions 7.2.0 through 7.2.8.1
- FTD versions 7.3.0 through 7.3.1.2
- FTD versions 7.4.1 through 7.4.2
Additional information is available through the Cisco ERP Alert Notification.
Workarounds
- No specific workarounds are documented by Cisco; applying patches is the recommended remediation
- Implement network segmentation to limit exposure of Firepower 2100 appliances to untrusted traffic
- Deploy additional perimeter filtering to reduce malicious packet delivery to vulnerable devices
- Establish runbooks for rapid manual reload procedures to minimize downtime during exploitation attempts
# Verify current FTD software version on Firepower appliance
show version
# Check Snort engine status and recent restart events
show snort statistics
show snort engine status
# Monitor for Snort crash events in system logs
show logging | include snort
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
