CVE-2018-0138 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 file policies that are configured to block files transmitted to an affected device via the BitTorrent protocol. The vulnerability exists because the affected software does not detect BitTorrent handshake messages correctly. An attacker could exploit this vulnerability by sending a crafted BitTorrent connection request to an affected device. A successful exploit could allow the attacker to bypass file policies that are configured to block files transmitted to the affected device via the BitTorrent protocol. Cisco Bug IDs: CSCve26946.
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Analysis
by VulDB Data Team • 02/03/2021
The vulnerability identified as CVE-2018-0138 resides within the detection engine of Cisco Firepower System Software, representing a critical flaw that undermines the security posture of networked environments relying on this protection platform. This weakness specifically targets the software's ability to properly identify and process BitTorrent protocol communications, creating an exploitable condition that allows malicious actors to circumvent configured file blocking policies. The vulnerability's impact extends beyond simple protocol misidentification, as it fundamentally compromises the integrity of content filtering mechanisms that organizations depend upon to prevent unauthorized file transfers across their networks.
The technical root cause of this vulnerability stems from the affected software's inadequate handling of BitTorrent handshake messages within its detection engine. When a BitTorrent connection request is initiated, the system fails to properly parse or recognize the specific handshake sequence that defines legitimate BitTorrent communication patterns. This parsing failure occurs at the protocol level where the software should be identifying and categorizing incoming traffic based on established BitTorrent protocol specifications. The flaw manifests as a false negative condition where malicious BitTorrent traffic is incorrectly classified as benign or unrecognized, allowing the traffic to bypass the configured file blocking policies. This misclassification directly relates to CWE-254, which addresses weaknesses in protocol implementation that can lead to security bypasses through improper handling of communication protocols.
The operational impact of this vulnerability creates significant risk for organizations utilizing Cisco Firepower systems, as it enables remote attackers to bypass critical security controls without requiring authentication or specialized privileges. An attacker positioned outside the network perimeter can exploit this vulnerability by crafting and transmitting specifically formatted BitTorrent connection requests to the affected device. The successful exploitation results in complete bypass of file blocking policies that are designed to prevent the transmission of potentially malicious files through the BitTorrent protocol. This capability allows threat actors to deliver malware, unauthorized content, or other security risks directly to networked devices without triggering the expected security alerts or blocking mechanisms. The vulnerability essentially creates a backdoor pathway that undermines the fundamental purpose of content filtering and file policy enforcement within the network security infrastructure.
Organizations affected by this vulnerability face substantial risk exposure given that BitTorrent protocol usage remains prevalent for both legitimate and malicious file distribution activities. The remote nature of the exploit means that attackers can target systems from anywhere on the internet without requiring physical access or network credentials, making the attack surface extremely broad. The vulnerability's persistence in the detection engine suggests that it affects all versions of Cisco Firepower System Software where the BitTorrent protocol handling is implemented, potentially impacting a wide range of network security deployments. Security teams must recognize that this vulnerability can be exploited to bypass multiple layers of security controls, including content filtering, file type restrictions, and malware detection mechanisms that rely on proper protocol identification for effective enforcement.
Cisco has documented this vulnerability under Bug ID CSCve26946 and has released software updates to address the specific protocol handling issue within the detection engine. The recommended mitigation strategy involves applying the latest security patches and software updates provided by Cisco to ensure proper BitTorrent handshake message detection and classification. Organizations should also consider implementing additional network monitoring and anomaly detection measures to identify unusual BitTorrent traffic patterns that might indicate exploitation attempts. Network administrators should review their current file policy configurations to ensure that alternative detection mechanisms are in place, and consider implementing network segmentation to limit the potential impact of successful exploitation. The vulnerability demonstrates the importance of proper protocol implementation in network security devices and highlights the need for comprehensive testing of detection engines against various communication protocols to prevent security bypass scenarios. This issue aligns with ATT&CK technique T1071.004 which covers application layer protocol: bitTorrent, emphasizing the need for proper protocol handling in network security controls to prevent evasion of content filtering mechanisms.