CVE-1999-1481 is a medium severity vulnerability affecting Squid Web Proxy versions 1.0, 1.0novm, 1.1, 2.1, and 2.2.STABLE5 and below. Squid is a widely used caching and forwarding HTTP proxy server. This vulnerability arises when Squid is configured to use external authentication mechanisms. Specifically, an attacker can exploit the way Squid processes user credentials by injecting a newline character within the user/password pair. This newline injection allows the attacker to bypass access control checks, effectively circumventing authentication and gaining unauthorized access to the proxy services. The vulnerability does not require any authentication or user interaction and can be exploited remotely over the network. The CVSS score of 5.0 (medium) reflects that while the vulnerability impacts confidentiality by allowing unauthorized access, it does not directly affect integrity or availability. No patches are available for this vulnerability, and there are no known exploits in the wild. Given the age of the affected versions (released before 2000), modern Squid versions have addressed this issue, but legacy systems running these outdated versions remain vulnerable.

For European organizations, this vulnerability poses a risk primarily to those still operating legacy Squid proxy servers with external authentication enabled. Successful exploitation could allow unauthorized users to bypass access controls, potentially exposing internal network resources and sensitive data that rely on the proxy for access management. This could lead to data leakage or unauthorized use of network services. Although the vulnerability does not directly compromise data integrity or availability, the unauthorized access could facilitate further attacks or reconnaissance. Organizations in sectors with strict data protection requirements (e.g., finance, healthcare, government) may face compliance risks if unauthorized access leads to data exposure. The risk is mitigated in environments that have upgraded to newer Squid versions or use alternative proxy solutions.

Given that no official patches are available for the affected legacy versions, European organizations should prioritize upgrading to the latest stable Squid releases where this vulnerability is resolved. If upgrading is not immediately feasible, organizations should consider disabling external authentication in Squid or implementing additional access control layers outside of Squid to prevent unauthorized access. Network segmentation and strict firewall rules can limit exposure of the proxy server to trusted networks only. Additionally, monitoring proxy logs for unusual authentication patterns or access attempts can help detect exploitation attempts. Organizations should also review and update their proxy authentication configurations to ensure they do not accept malformed credentials containing newline characters. Finally, conducting regular vulnerability assessments and penetration tests can help identify legacy systems still vulnerable to this issue.