CVE-2025-20135 in ASA
Summary
by MITRE • 08/14/2025
A vulnerability in the DHCP client functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, adjacent attacker to exhaust available memory.
This vulnerability is due to improper validation of incoming DHCP packets. An attacker could exploit this vulnerability by repeatedly sending crafted DHCPv4 packets to an affected device. A successful exploit could allow the attacker to exhaust available memory, which would affect availability of services and prevent new processes from starting, resulting in a Denial of Service (DoS) condition that would require a manual reboot. Note: On Cisco Secure FTD Software, this vulnerability does not affect management interfaces.
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Analysis
by VulDB Data Team • 08/17/2025
This vulnerability resides within the dynamic host configuration protocol client implementation of Cisco's security appliances, specifically impacting the adaptive security appliance and threat defense software platforms. The flaw manifests as inadequate validation mechanisms for incoming dhcpv4 packets, creating a pathway for malicious actors to exploit the system's resource management capabilities. The vulnerability's classification aligns with common weakness enumeration cwe-20, which addresses improper input validation, and represents a significant concern for network infrastructure devices that must maintain continuous availability. The affected software components process dhcp client functionality to obtain network configuration parameters, making them susceptible to resource exhaustion attacks through malformed packet sequences.
The technical exploitation involves an adjacent attacker who can send repeated crafted dhcpv4 packets to the targeted appliance, leveraging the insufficient validation controls to consume available memory resources. This type of attack demonstrates characteristics consistent with the attack technique t1499.004 from the attack tactics and techniques framework, specifically targeting network denial of service conditions through resource exhaustion. The vulnerability's impact occurs at the network protocol level where dhcp client implementations fail to properly validate packet structures, lengths, or sequence numbers, allowing attackers to craft packets that trigger memory allocation without proper cleanup mechanisms. The memory exhaustion occurs gradually through repeated packet submissions, with each malicious packet consuming system resources until the appliance reaches its memory capacity limits.
Operational consequences of this vulnerability extend beyond simple service disruption, creating cascading effects that can compromise overall network security posture. When available memory is exhausted, the affected appliance cannot process new network traffic, establish new connections, or maintain existing sessions, effectively rendering the security device non-functional until manual intervention occurs through system reboot. This requirement for manual reboot represents a significant operational burden, particularly in environments where continuous network security is critical. The vulnerability's impact is particularly concerning for organizations relying on these appliances for network segmentation, intrusion prevention, and traffic control functions, as the device failure could create security gaps in the network infrastructure. The fact that management interfaces remain unaffected on ftd software versions provides partial mitigation but does not address the core operational disruption caused by the memory exhaustion attack.
Mitigation strategies should prioritize immediate software updates from cisco to address the validation flaws in dhcp client processing. Organizations must implement network segmentation to limit adjacent access to these devices, reducing the attack surface available to potential adversaries. Network monitoring solutions should be configured to detect unusual dhcp packet patterns and trigger alerts when memory consumption spikes occur. Additionally, implementing rate limiting controls on dhcp client processing can help prevent the rapid packet flooding that leads to memory exhaustion. The vulnerability's characteristics suggest that defensive measures should include both preventive software patches and reactive monitoring capabilities to detect and respond to exploitation attempts. Security teams should also consider implementing redundant security appliances to maintain network protection during potential outages caused by this vulnerability.