CVE-2023-20177 in Firepower Threat Defense Software
Summary
by MITRE • 11/01/2023
A vulnerability in the SSL file policy implementation of Cisco Firepower Threat Defense (FTD) Software that occurs when the SSL/TLS connection is configured with a URL Category and the Snort 3 detection engine could allow an unauthenticated, remote attacker to cause the Snort 3 detection engine to unexpectedly restart. This vulnerability exists because a logic error occurs when a Snort 3 detection engine inspects an SSL/TLS connection that has either a URL Category configured on the SSL file policy or a URL Category configured on an access control policy with TLS server identity discovery enabled. Under specific, time-based constraints, an attacker could exploit this vulnerability by sending a crafted SSL/TLS connection through an affected device. A successful exploit could allow the attacker to trigger an unexpected reload of the Snort 3 detection engine, resulting in either a bypass or denial of service (DoS) condition, depending on device configuration. The Snort 3 detection engine will restart automatically. No manual intervention is required.
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Analysis
by VulDB Data Team • 11/29/2023
This vulnerability resides within the SSL file policy implementation of Cisco Firepower Threat Defense software, specifically affecting the Snort 3 detection engine's handling of SSL/TLS connections. The flaw manifests when SSL/TLS connections are configured with URL Category settings, creating a condition where the detection engine experiences a logic error during inspection processes. The vulnerability represents a critical weakness in the software's traffic processing capabilities, as it directly impacts the stability and reliability of the network security infrastructure.
The technical root cause stems from a logic error within the Snort 3 detection engine's inspection routines when processing SSL/TLS connections that have URL Category configurations applied either through SSL file policies or access control policies with TLS server identity discovery enabled. This condition creates a scenario where the detection engine encounters malformed or unexpected data patterns during connection inspection, leading to an unexpected restart of the engine. The vulnerability operates under specific time-based constraints that must be met for successful exploitation, making it particularly insidious as it requires precise timing and network conditions to trigger.
The operational impact of this vulnerability extends beyond simple service disruption, as it creates potential bypass scenarios or denial of service conditions depending on the device's configuration. When the Snort 3 detection engine restarts unexpectedly, it temporarily removes the network traffic inspection capabilities that the engine provides, leaving the network potentially exposed to threats that would normally be detected. The automatic restart feature means that the device does not require manual intervention, but this also means that the disruption occurs without administrator awareness, potentially allowing attackers to exploit the vulnerability multiple times without detection.
This vulnerability aligns with CWE-248, which addresses "Uncaught Exception" conditions in software implementations, and represents a specific instance where an unhandled logic error leads to system instability. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, "Endpoint Denial of Service," and potentially T1566.001, "Phishing," as attackers could use the DoS condition to disrupt legitimate network operations or create cover for other attacks. The remote and unauthenticated nature of the exploit means that adversaries can leverage this weakness without requiring privileged access or specific credentials, making it particularly dangerous in network security contexts.
Mitigation strategies should focus on immediate software updates from Cisco to address the underlying logic error in the Snort 3 detection engine. Network administrators should also implement monitoring solutions to detect unusual engine restart patterns that could indicate exploitation attempts. Additionally, temporary workarounds such as removing URL Category configurations from SSL file policies or access control policies with TLS server identity discovery could provide immediate protection while permanent fixes are deployed. The vulnerability highlights the importance of proper exception handling in network security appliances and demonstrates how seemingly minor logic errors in detection engines can create significant operational impacts.