CVE-1999-0777 in IIS
Summary
by MITRE
IIS FTP servers may allow a remote attacker to read or delete files on the server, even if they have "No Access" permissions.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0777 represents a critical access control flaw in Microsoft Internet Information Services FTP servers that persisted through multiple versions of the software. This weakness fundamentally undermines the security model of file access controls by allowing unauthorized remote attackers to bypass permission restrictions that should prevent file access. The vulnerability specifically affects the FTP service component of IIS, which was widely deployed in enterprise environments during the late 1990s and early 2000s, making it a significant concern for organizations relying on web and file server infrastructure.
The technical flaw manifests in the way IIS FTP servers handle access control lists and permission validation during file operations. When users attempt to perform read or delete operations on files through the FTP protocol, the server fails to properly validate whether the requesting user possesses sufficient privileges according to the configured permissions. This allows an attacker to exploit the FTP service and access files that should be restricted based on the "No Access" permission setting, effectively bypassing the intended security controls. The vulnerability operates at the protocol level where the FTP service does not properly enforce the access control mechanisms that should govern file system interactions.
The operational impact of this vulnerability extends far beyond simple unauthorized file access, as it provides attackers with the capability to not only read sensitive files but also delete critical system components or data. This represents a severe privilege escalation scenario where attackers can compromise entire file systems and potentially gain persistent access to server resources. The vulnerability's remote nature means that attackers do not require physical access or local credentials to exploit the flaw, making it particularly dangerous in networked environments where FTP services are exposed to external networks. Security professionals noted that this vulnerability could enable attackers to escalate privileges and potentially compromise the entire server infrastructure.
Mitigation strategies for this vulnerability focused primarily on immediate patch deployment from Microsoft, which provided security updates to address the access control bypass issue. Organizations were advised to implement network segmentation to limit exposure of FTP services to untrusted networks and to disable unnecessary FTP services where possible. The vulnerability highlighted the importance of proper access control implementation in web server software and led to enhanced security practices in subsequent software development cycles. This issue contributed to the broader understanding of secure coding practices and the need for comprehensive input validation in network services, aligning with principles found in CWE-284 which addresses improper access control vulnerabilities. Additionally, the vulnerability demonstrated the importance of implementing defense-in-depth strategies and proper network access controls as outlined in ATT&CK framework's privilege escalation techniques, where attackers could leverage weak access controls to move laterally within compromised environments. Organizations were also encouraged to implement monitoring solutions to detect anomalous FTP access patterns that might indicate exploitation attempts, and to conduct regular security assessments to identify similar access control weaknesses in other network services.