CVE-1999-0524 is a vulnerability related to the handling of certain ICMP (Internet Control Message Protocol) information messages by affected Apple Mac OS X systems. Specifically, the vulnerability allows ICMP information requests such as netmask and timestamp queries to be accepted from arbitrary hosts without restriction. ICMP netmask requests are used to determine the subnet mask of a target host, while ICMP timestamp requests provide timing information about the target system. Allowing these requests from any source can lead to unintended information disclosure. The vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The CVSS v2 score is 2.1, indicating a low severity level, with the vector AV:L/AC:L/Au:N/C:P/I:N/A:N, meaning the attack requires local access, low complexity, no authentication, and impacts confidentiality only, without affecting integrity or availability. No patches are available, and there are no known exploits in the wild. Given the age of this vulnerability (published in 1997) and the lack of patch availability, it is likely that modern versions of Mac OS X have addressed this issue or that it is no longer relevant in current deployments. However, in legacy or unpatched systems, this vulnerability could allow an attacker with local network access to gather network topology and timing information, which could be used for reconnaissance or to aid in further attacks.

For European organizations, the impact of this vulnerability is limited due to its low severity and the requirement for local network access to exploit it. The primary risk is information disclosure, specifically network configuration details and system timing, which could assist attackers in mapping internal networks or conducting timing-based attacks. While this does not directly compromise system integrity or availability, it could facilitate more targeted attacks if combined with other vulnerabilities. Organizations with legacy Apple Mac OS X systems that are unpatched or isolated from external networks may still be at risk. However, modern network security practices, including segmentation, firewall rules, and intrusion detection, reduce the likelihood of exploitation. The vulnerability does not pose a significant threat to cloud or virtualized environments unless legacy Mac OS X systems are present.

Given the absence of an official patch, European organizations should implement network-level controls to mitigate this vulnerability. Specifically, they should configure firewalls and intrusion prevention systems to block or restrict ICMP information request messages (types 1 and 13) from untrusted or external sources. Network segmentation should be enforced to limit local network access to critical Mac OS X systems. Additionally, organizations should audit their environments to identify any legacy Mac OS X systems and consider upgrading or isolating them. Monitoring network traffic for unusual ICMP activity can help detect reconnaissance attempts. Finally, educating network administrators about the risks of ICMP information requests and ensuring that security policies explicitly address ICMP traffic handling will further reduce exposure.