CVE-1999-0777 is a high-severity vulnerability affecting Microsoft IIS FTP servers, specifically versions 2.5 and 4.0. This vulnerability allows a remote attacker to bypass file access permissions, enabling unauthorized reading or deletion of files on the FTP server. The flaw arises because the FTP server improperly enforces access controls, permitting attackers to perform file operations even when their permissions are set to "No Access." The vulnerability is exploitable remotely without requiring authentication (AV:N/Au:N), with low attack complexity (AC:L), and impacts confidentiality, integrity, and availability (C:P/I:P/A:P). This means an attacker can fully compromise file data by reading sensitive files or deleting critical files, potentially disrupting services or exposing confidential information. Although this vulnerability dates back to 1999 and affects legacy IIS FTP server versions, it remains relevant in environments where outdated systems are still operational. Microsoft has released patches to address this issue, documented in security bulletin MS99-039. No known exploits have been reported in the wild, but the ease of exploitation and the severity of impact make it a significant risk if unpatched.

For European organizations, this vulnerability poses a substantial risk, especially for those still running legacy IIS FTP servers (versions 2.5 and 4.0) in their infrastructure. Exploitation could lead to unauthorized disclosure of sensitive files, including personal data protected under GDPR, resulting in compliance violations and potential fines. Additionally, the ability to delete files can disrupt business operations, cause data loss, and damage organizational reputation. Sectors such as government, healthcare, finance, and critical infrastructure in Europe, which may have legacy systems due to long upgrade cycles or specialized applications, are particularly vulnerable. The remote and unauthenticated nature of the attack vector increases the threat surface, making it easier for attackers to exploit without insider access. Even though no active exploits are currently known, the vulnerability's age and severity warrant immediate attention to prevent potential targeted attacks or opportunistic scanning by threat actors.

European organizations should prioritize identifying any IIS FTP servers running versions 2.5 or 4.0 within their networks. Immediate mitigation steps include applying the official Microsoft patches provided in security bulletin MS99-039 to remediate the vulnerability. If patching is not immediately feasible, organizations should consider disabling the affected FTP services or restricting FTP access via network segmentation and firewall rules to limit exposure. Implementing strict monitoring and logging of FTP server activity can help detect suspicious access attempts. Additionally, migrating to modern, supported FTP server software or alternative secure file transfer protocols (e.g., SFTP or FTPS) is recommended to reduce reliance on vulnerable legacy systems. Regular vulnerability assessments and audits should be conducted to ensure no outdated IIS FTP servers remain in production environments.