CVE-2026-123784 in Fluxbox
Summary
by MITRE • 11/06/2026
Fluxbox through 1.3.7 contains an OS command injection vulnerability in RootTheme::reconfigTheme() that allows attackers to execute commands via crafted style background values. Attackers can embed shell metacharacters in background pixmap paths, random directories, or gradient texture text, which are concatenated unescaped into an fbsetbg command run via $SHELL -c when the style loads.
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Analysis
by VulDB Data Team • 11/06/2026
The vulnerability identified in Fluxbox versions through 1.3.7 represents a critical OS command injection flaw located within the RootTheme::reconfigTheme() function. This security issue stems from improper neutralization of special elements used in an operating system command, specifically categorized under CWE-78 as Improper Neutralization of Special Elements used in an OS Command. The root cause lies in how the application processes user-supplied input related to theme styling configurations. When a new style is loaded or reconfigured, the software constructs shell commands by concatenating various string components without performing adequate sanitization or escaping procedures on potentially malicious data embedded within those strings.
The specific attack vector involves manipulating background configuration parameters such as pixmap paths, random directory names, and gradient texture text definitions. An attacker who has access to modify these theme settings can inject shell metacharacters into any of these fields. Because the application subsequently passes this unescaped input directly to a system call using $SHELL -c, the injected characters are interpreted by the underlying operating system's command interpreter rather than being treated as literal string data. This allows for the execution of arbitrary commands with the privileges associated with the user running the Fluxbox session.
The operational impact of this vulnerability is severe due to its potential for remote code execution within the context of the desktop environment. Since Fluxbox is a window manager, successful exploitation could allow an attacker to gain control over the user's session, potentially leading to data theft, installation of malware, or further lateral movement if other services are accessible from that account. The vulnerability affects the integrity and confidentiality of the system by bypassing standard input validation mechanisms inherent in secure software design practices.
Mitigation strategies primarily involve upgrading Fluxbox to version 1.3.8 or later where this issue has been addressed through proper input sanitization and command construction methods. In environments where immediate patching is not feasible, administrators should restrict who can modify theme configuration files and enforce strict access controls on style directories. Additionally, employing application whitelisting solutions such as SELinux or AppArmor can help limit the damage caused by any successful exploitation attempt by restricting the shell commands that can be executed in specific contexts. This incident highlights the importance of adhering to secure coding standards regarding command execution and input validation, aligning with broader industry guidelines for preventing injection-based attacks.