CVE-1999-1550 is a medium-severity vulnerability affecting F5 BIG/ip devices running TMOS version 2.1.2 and earlier, specifically version 2.0 as noted. The vulnerability arises from improper access control in the bigconf.conf configuration file handler, which allows remote attackers to read arbitrary files on the affected device. This is achieved by specifying the target file path in the "file" parameter of a request, which the system then processes without sufficient validation or restriction. As a result, an unauthenticated attacker can remotely retrieve sensitive configuration files or other critical system files, potentially exposing sensitive information such as credentials, network configurations, or other operational data. The vulnerability does not allow modification or disruption of system availability, but the confidentiality breach can facilitate further attacks or reconnaissance. The CVSS v2 score is 5.0 (medium), with the vector AV:N/AC:L/Au:N/C:P/I:N/A:N indicating network attack vector, low attack complexity, no authentication required, partial confidentiality impact, and no integrity or availability impact. No patches are available for this vulnerability, and no known exploits have been reported in the wild, likely due to the age of the affected software and its limited deployment today. However, legacy systems still running these versions remain at risk.

For European organizations, the primary impact of this vulnerability is the potential exposure of sensitive configuration and operational data from F5 BIG/ip devices running vulnerable TMOS versions. Such data leakage can compromise network security by revealing internal network topology, authentication credentials, or other sensitive operational parameters. This can facilitate lateral movement, targeted attacks, or unauthorized access to critical infrastructure. While the vulnerability does not directly allow system compromise or denial of service, the confidentiality breach can be leveraged in multi-stage attacks. Organizations in sectors with high reliance on F5 BIG/ip devices for load balancing and application delivery—such as finance, telecommunications, government, and critical infrastructure—may face increased risk. The lack of available patches means that mitigation relies on compensating controls or upgrading to supported versions. Given the age of the vulnerability and the product versions affected, the impact is primarily on legacy systems that have not been updated or replaced, which may still exist in some European enterprises or public sector networks.

Since no patches are available for this vulnerability, European organizations should prioritize the following mitigation steps: 1) Identify and inventory all F5 BIG/ip devices in their environment, specifically checking for TMOS versions 2.1.2 and earlier. 2) Upgrade or replace legacy devices running vulnerable versions with supported, updated TMOS versions where this vulnerability is resolved. 3) If upgrading is not immediately feasible, restrict network access to management interfaces and configuration files by implementing strict firewall rules and network segmentation to limit exposure to trusted administrative hosts only. 4) Monitor network traffic for unusual requests targeting the bigconf.conf file or attempts to access arbitrary files via the "file" parameter. 5) Employ intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics to detect exploitation attempts. 6) Conduct regular security audits and vulnerability assessments to identify legacy devices and ensure compliance with security policies. 7) Educate network and security teams about the risks associated with legacy F5 devices and the importance of timely updates or replacements.