CVE-2020-25014 in UTM
Summary
by MITRE • 11/27/2020
A stack-based buffer overflow in fbwifi_continue.cgi on Zyxel UTM and VPN series of gateways running firmware version V4.30 through to V4.55 allows remote unauthenticated attackers to execute arbitrary code via a crafted http packet.
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Analysis
by VulDB Data Team • 12/12/2024
The vulnerability identified as CVE-2020-25014 represents a critical stack-based buffer overflow flaw in the fbwifi_continue.cgi component of Zyxel UTM and VPN series gateways. This vulnerability affects firmware versions ranging from V4.30 through V4.55, creating a substantial attack surface for remote unauthenticated adversaries who can exploit this weakness without requiring any credentials or prior access to the network. The flaw resides within the web interface processing logic of these network security appliances, specifically in how they handle HTTP requests directed to the fbwifi_continue.cgi script.
The technical nature of this vulnerability stems from improper input validation within the fbwifi_continue.cgi script which fails to adequately check the length of user-supplied data before copying it onto a fixed-size stack buffer. When an attacker crafts a malicious HTTP packet containing oversized data in specific parameters, the application continues to copy this data beyond the allocated buffer boundaries, resulting in a stack overflow condition. This type of vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a high-severity issue in the Common Weakness Enumeration catalog due to its potential for arbitrary code execution. The overflow occurs during the processing of HTTP requests, making it particularly dangerous as it can be triggered through standard web traffic without requiring any authentication or privileged access.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with complete control over the affected network appliances. Once exploited, an attacker gains the ability to execute arbitrary commands with the privileges of the web server process, which typically runs with elevated permissions on the device. This could lead to complete system compromise, allowing attackers to install backdoors, modify firewall rules, redirect traffic, or use the compromised device as a pivot point for attacking internal network resources. The vulnerability affects Zyxel UTM and VPN series gateways, which are commonly deployed in enterprise and small to medium business environments, making the potential impact widespread. These devices serve as critical network security infrastructure, and their compromise could result in significant data breaches, network disruption, and loss of security controls. The remote unauthenticated nature of the attack means that adversaries can exploit this vulnerability from anywhere on the internet without needing physical access to the device or knowledge of valid credentials, making it particularly dangerous for organizations with exposed internet-facing devices.
Organizations should implement immediate mitigations to address this vulnerability, beginning with firmware updates from Zyxel that contain patches for the buffer overflow condition. The company released firmware versions containing fixes for this issue, and administrators should prioritize upgrading to these patched versions as soon as possible. Network segmentation and access control measures should be implemented to limit exposure of these devices to untrusted networks, particularly by blocking direct internet access to the affected web interface ports. Monitoring network traffic for suspicious HTTP requests that match the exploit patterns can help detect attempted exploitation of this vulnerability. Security teams should also consider implementing intrusion detection systems with signatures specific to this vulnerability, as well as conducting thorough vulnerability assessments of their network infrastructure to identify any other potentially affected devices. The ATT&CK framework categorizes this type of vulnerability exploitation under T1059 Command and Scripting Interpreter and T1068 Exploitation for Privilege Escalation, highlighting the potential for attackers to leverage such flaws to gain persistent access to network resources and escalate their privileges within the compromised environment. Organizations should also review their incident response procedures to ensure they can quickly detect and respond to exploitation attempts targeting this specific vulnerability.