CVE-1999-0491 is a medium-severity vulnerability affecting multiple early versions of the GNU Bash shell, specifically versions 1.14.0 through 1.14.7 and 2.0 through 2.05. The vulnerability arises from the way Bash parses the command prompt string (PS1). In these affected versions, a local user can exploit the prompt parsing mechanism by creating a directory named after a command they wish to execute. When Bash processes the prompt, it inadvertently executes commands embedded in directory names, allowing the attacker to run arbitrary commands with the privileges of another user. This vulnerability is a form of code injection related to CWE-94 (Improper Control of Generation of Code). The attack requires local access and does not require authentication, but it does require the attacker to have the ability to create directories in a location that influences the prompt parsing of the target user. There is no patch available for this vulnerability, and no known exploits have been reported in the wild. The CVSS v2 score is 4.6, reflecting a medium severity with local attack vector, low attack complexity, no authentication required, and partial impact on confidentiality, integrity, and availability.

For European organizations, the impact of this vulnerability is primarily on systems running legacy versions of Bash, which are now very old and generally replaced in modern environments. However, in environments where legacy Unix/Linux systems are still in use, this vulnerability could allow a local attacker to escalate privileges or execute arbitrary commands as another user, potentially leading to unauthorized access to sensitive data, system compromise, or disruption of services. The vulnerability affects confidentiality, integrity, and availability to a partial extent. Although exploitation requires local access, insider threats or attackers who have gained limited access could leverage this flaw to expand their control. Given the age of the vulnerability and lack of patches, organizations relying on legacy systems without updates are at risk. For modern European enterprises, the direct risk is low, but legacy industrial control systems, embedded devices, or specialized environments might still be vulnerable.

Since no official patch is available for the affected Bash versions, European organizations should prioritize upgrading to a modern, supported version of Bash where this vulnerability has been addressed. For legacy systems where upgrading is not immediately feasible, organizations should restrict local user permissions to prevent unauthorized directory creation in locations that influence prompt parsing. Implement strict access controls and monitoring on systems with legacy Bash versions to detect suspicious directory creation or command execution patterns. Employ application whitelisting and intrusion detection systems to identify anomalous behavior indicative of exploitation attempts. Additionally, consider isolating legacy systems from critical networks and limiting local user access to trusted personnel only. Regular audits of system configurations and user permissions can help reduce the attack surface. Finally, organizations should maintain comprehensive logging to facilitate forensic analysis in case of suspected exploitation.