CVE-2021-1402 in Firepower Threat Defense
Summary
by MITRE • 04/30/2021
A vulnerability in the software-based SSL/TLS message handler of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message through an affected device. SSL/TLS messages sent to an affected device do not trigger this vulnerability. A successful exploit could allow the attacker to cause a process to crash. This crash would then trigger a reload of the device. No manual intervention is needed to recover the device after the reload.
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Analysis
by VulDB Data Team • 05/03/2021
This vulnerability resides within the software-based SSL/TLS message handling component of Cisco Firepower Threat Defense (FTD) software, representing a critical weakness that enables unauthenticated remote attackers to induce device reloads and subsequently cause denial of service conditions. The flaw specifically manifests when the device engages in software-based SSL decryption processes, creating an exploitable condition that bypasses normal authentication requirements. The vulnerability stems from inadequate validation mechanisms within the SSL/TLS message processing pipeline, allowing malformed or specially crafted messages to pass through without proper scrutiny. This represents a fundamental failure in input validation and message integrity checking that directly impacts the device's stability and operational continuity. The issue is particularly concerning because it operates entirely within the network layer processing without requiring any prior authentication credentials or privileged access.
The technical exploitation mechanism involves sending specifically crafted SSL/TLS messages to the affected FTD device, where the software-based decryption engine fails to properly validate incoming message structures. When these malformed messages are processed, they trigger an internal error condition that causes a specific process to crash unexpectedly. This process failure is not merely a minor glitch but a critical system failure that cascades into a complete device reload sequence. The crash occurs during the SSL/TLS message handling phase, specifically when the software engine attempts to parse or decrypt the malicious input. The vulnerability's design flaw lies in the absence of proper bounds checking, input sanitization, and error recovery mechanisms within the SSL/TLS processing module. This type of vulnerability maps directly to CWE-129, Input Validation, and CWE-248, Uncaught Exception, as it involves both improper input handling and failure to properly manage exceptional conditions. The exploitation process follows ATT&CK technique T1499.004, Network Denial of Service, by leveraging the device's own processing capabilities to generate the destructive reload condition.
The operational impact of this vulnerability extends far beyond simple service interruption, as it creates a persistent threat to network availability and security operations. Network administrators face the challenge of maintaining continuous protection while dealing with potential automated exploitation attempts that could occur without any indication of compromise. The automatic reload mechanism provides no opportunity for manual intervention or recovery procedures, meaning that network availability is immediately compromised for the duration of the restart cycle. This vulnerability affects the core functionality of the FTD appliance, which serves as a critical security gateway for network traffic inspection and threat prevention. The device's ability to maintain consistent operation becomes compromised, potentially exposing network segments to attack during the brief window when the device is restarting. The lack of manual recovery requirements means that the system automatically returns to operation, but this automatic process may not be visible to network operators, creating a potential blind spot in security monitoring. Organizations relying on FTD appliances for network security may experience service degradation or complete loss of security inspection capabilities, depending on the frequency and timing of exploitation attempts. The vulnerability essentially allows an attacker to perform a remote denial of service attack that requires no specialized tools or credentials, making it particularly dangerous in environments where such devices form the primary security perimeter. This represents a significant concern for organizations that depend on continuous network protection and may have compliance requirements that mandate high availability of security infrastructure. The vulnerability's impact is amplified by its ability to cause automatic device restarts, which could be leveraged in coordinated attacks against multiple devices within the same network segment, potentially creating cascading failures across security infrastructure.