CVE-2026-20101 in Secure Firewall Adaptive Security Appliance Software
Summary
by MITRE • 03/04/2026
A vulnerability in the SAML 2.0 single sign-on (SSO) feature of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a DoS condition. This vulnerability is due to insufficient error checking when processing SAML messages. An attacker could exploit this vulnerability by sending crafted SAML messages to the SAML service. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 05/02/2026
This vulnerability resides within the SAML 2.0 single sign-on implementation of Cisco Secure Firewall ASA Software and Secure FTD Software, representing a critical denial-of-service weakness that can be exploited remotely without authentication. The flaw manifests as inadequate input validation and error handling mechanisms when processing SAML authentication messages, creating a pathway for malicious actors to disrupt network security operations. The vulnerability specifically affects the SAML service component that handles authentication requests from identity providers, where proper validation of incoming SAML assertions and responses is insufficient to prevent malformed or crafted inputs from causing system instability.
The technical exploitation of this vulnerability occurs through the injection of specially crafted SAML messages that trigger buffer overflows or memory corruption within the SAML processing module. When the firewall software receives these malformed messages, the insufficient error checking routines fail to properly validate the message structure, length, or content, allowing the malformed data to propagate through the processing pipeline. This lack of proper input sanitization and validation creates a condition where the application's memory management routines become corrupted, ultimately leading to the device's unexpected restart or reload. The vulnerability is classified as a weakness in input validation and error handling, aligning with CWE-20, which addresses improper input validation, and CWE-129, which covers insufficient validation of length of input buffers.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise network availability and security posture. Network administrators face the risk of unauthorized disruption of their security infrastructure, potentially creating windows of vulnerability during device restart periods. The DoS condition affects the entire firewall appliance, potentially blocking legitimate network traffic while the device reboots, and may provide attackers with opportunities to escalate their attack surface. From an operational security perspective, this vulnerability directly impacts the CIA triad, specifically compromising availability of the security infrastructure and potentially creating conditions where attackers can bypass security controls during the device reload process.
Organizations should implement immediate mitigations including network segmentation to restrict access to SAML services, disabling unused SAML functionality when possible, and implementing network monitoring to detect unusual traffic patterns that may indicate exploitation attempts. The vulnerability's remote and unauthenticated nature means that any device with SAML services enabled represents a potential attack surface, making proactive network monitoring essential. Security teams should consider implementing intrusion detection systems that can identify and alert on malformed SAML messages, while also ensuring that all devices are updated with the latest security patches from Cisco. According to ATT&CK framework, this vulnerability maps to T1499.004 for endpoint resource exhaustion and T1566.002 for malicious SAML messages, highlighting the need for comprehensive endpoint protection and identity service monitoring. The vulnerability underscores the importance of robust input validation practices and proper error handling in security-critical applications, particularly in identity management systems where malformed inputs can have cascading effects on system stability and availability.