CVE-2023-43826: Integer Overflow in Apache Guacamole Opens Door to RCE

A vulnerability has recently been identified in Apache Guacamole, an HTML5 web application that provides access to desktop environments using remote desktop protocols (such as VNC or RDP). Guacamole is also the project that produces this web application and provides an API that drives it. This API can be used to power other similar applications or services.

Tagged as CVE-2023-43826 and rated with a concerning CVSS score of 7.5, this security flaw in Apache Guacamole represents a significant threat. Specifically, versions 1.5.3 and earlier are prone to an integer overflow in the handling of VNC image buffers. This seemingly minor lapse in data handling can have major repercussions.

At its core, the issue stems from an integer overflow vulnerability. This occurs when a value exceeds the maximum capacity that a variable can hold, causing the value to wrap around to a negative number or zero. In the context of Apache Guacamole, this flaw arises when values received from a VNC server are not properly checked, leading to potential memory corruption.

The cascade from a simple integer overflow to memory corruption is a hacker‘s intention. By connecting to a malicious or compromised VNC server, attackers can exploit this flaw to execute arbitrary code with the privileges of the running guacd process. This opens a potential security breach, ranging from data theft to system takeovers.

The identification of CVE-2023-43826 can be credited to the security researchers Joseph Surin and Matt Jones from Elttam.

Apache Guacamole version 1.5.4 has been released to address this vulnerability, patching the security hole and fortifying the defenses against potential exploitation.