CVE-2018-0244 in Firepower System Software
Summary
by MITRE
A vulnerability in the detection engine of Cisco Firepower System Software could allow an unauthenticated, remote attacker to bypass a configured file action policy to drop the Server Message Block (SMB) protocol if a malware file is detected. The vulnerability is due to how the SMB protocol handles a case in which a large file transfer fails. This case occurs when some pieces of the file are successfully transferred to the remote endpoint, but ultimately the file transfer fails and is reset. An attacker could exploit this vulnerability by sending a crafted SMB file transfer request through the targeted device. An exploit could allow the attacker to pass an SMB file that contains malware, which the device is configured to block. This vulnerability affects Cisco Firepower System Software when one or more file action policies are configured, on software releases prior to 6.2.3. Cisco Bug IDs: CSCvc20141.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 08/12/2026
The vulnerability described in CVE-2018-0244 represents a critical flaw in Cisco Firepower System Software that undermines the integrity of file inspection and blocking mechanisms. This weakness resides within the detection engine's handling of Server Message Block protocol traffic, specifically when dealing with failed large file transfers. The vulnerability stems from improper state management during SMB file transfer operations where the system fails to correctly process partial transfers that ultimately fail and reset. According to the Cisco Bug ID CSCvc20141, this issue affects devices running software releases prior to version 6.2.3, making it a persistent threat across multiple deployment scenarios where organizations have not yet applied the necessary security patches. The flaw essentially creates a bypass mechanism that allows malicious SMB file transfers to evade configured security policies, undermining the fundamental purpose of network security appliances.
The technical exploitation of this vulnerability occurs through carefully crafted SMB file transfer requests that trigger the specific edge case in the detection engine's processing logic. When an attacker sends an SMB request that results in a partial file transfer failure, the system's internal state machine fails to properly classify or block the malicious file content that was successfully transmitted before the transfer failure. This creates a window of opportunity where malware can traverse the network security controls that should have intercepted and blocked the file based on configured file action policies. The vulnerability operates at the protocol level, specifically targeting the SMB implementation within the Firepower system's inspection engine, making it particularly dangerous as it bypasses traditional content inspection mechanisms. The flaw demonstrates a classic case of improper error handling and state management that allows security controls to be circumvented through protocol-specific edge cases.
The operational impact of this vulnerability extends beyond simple policy bypass, as it fundamentally compromises the trust model of network security appliances. Organizations relying on Cisco Firepower systems for SMB traffic inspection and blocking may experience unauthorized malware delivery and execution within their networks, potentially leading to lateral movement, data exfiltration, or complete system compromise. The vulnerability affects the core security functionality of the device, meaning that even properly configured file action policies become ineffective against targeted attacks. This weakness particularly impacts enterprise environments where SMB protocol usage is common for file sharing and business operations, creating a significant attack surface for threat actors who understand how to leverage protocol edge cases. The remote nature of the exploit means that attackers can target vulnerable devices from outside the network perimeter, amplifying the potential impact and reducing the difficulty of exploitation.
Mitigation strategies for this vulnerability require immediate patching of affected Cisco Firepower devices to software version 6.2.3 or later, as recommended by Cisco security advisories. Network administrators should also implement additional monitoring and logging mechanisms to detect anomalous SMB traffic patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol usage and CWE-252 for unchecked return values, highlighting the need for comprehensive input validation and proper error handling in security appliances. Organizations should also consider implementing network segmentation and additional layers of security controls to reduce the impact if exploitation occurs. Regular security assessments and vulnerability scanning should be conducted to identify other potential protocol-specific edge cases that might exist in similar network security devices. The remediation process must include thorough testing of the patched software to ensure that legitimate SMB traffic continues to function properly while maintaining the security protections that were previously compromised by this vulnerability.