Cisco Firepower Threat Defense Software NULL Character Obfuscation Detection Bypass Vulnerability

Vulnerability

CVE-2019-1981 is an obfuscation-based detection bypass vulnerability in the normalization functionality of Cisco Firepower Threat Defense (FTD) Software, Cisco FirePOWER Services Software for ASA, and Cisco Firepower Management Center (FMC) Software [1]. The flaw is due to insufficient normalization of text-based payloads that contain NULL characters. At the time of publication, all releases of the affected products were considered vulnerable [1].

Exploitation

An unauthenticated, remote attacker can exploit the vulnerability by sending network traffic that includes specifically obfuscated payloads through an affected device [1]. No authentication or privileged access is required; the attacker only needs the ability to send crafted traffic to a protected network segment.

Impact

Successful exploitation allows the attacker to bypass the device's filtering protections, delivering malicious payloads to protected systems that would otherwise be blocked [1]. This could lead to further compromise of downstream hosts, including potential information disclosure, malware delivery, or other unauthorized actions, depending on the nature of the obfuscated payload.

Mitigation

Cisco has not released software updates to address this vulnerability; no fixed version existed as of the advisory publication date [1]. No workarounds are available [1]. Users should monitor Cisco Security Advisories for future updates and consider upgrading to a patched release when one becomes available.