CVE-2001-1500 in ProFTPD
Summary
by MITRE
ProFTPD 1.2.2rc2, and possibly other versions, does not properly verify reverse-resolved hostnames by performing forward resolution, which allows remote attackers to bypass ACLs or cause an incorrect client hostname to be logged.
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Analysis
by VulDB Data Team • 05/22/2019
The vulnerability identified as CVE-2001-1500 affects ProFTPD version 1.2.2rc2 and potentially other versions within the same release cycle, representing a significant security flaw in the handling of client hostname resolution. This issue stems from the software's improper verification mechanism for reverse-resolved hostnames, creating a critical gap in access control and logging mechanisms. The flaw manifests when the system performs reverse DNS lookups to determine client hostnames but fails to validate these results through forward resolution checks, allowing malicious actors to exploit this weakness for unauthorized access.
The technical implementation of this vulnerability involves the FTP daemon's hostname resolution process where it accepts reverse DNS lookup results without proper validation against forward DNS resolution. This creates a scenario where an attacker can manipulate the hostname resolution process to bypass Access Control Lists that rely on hostname-based restrictions. When the server performs reverse DNS resolution to determine a client's hostname, it should verify that the reverse lookup result corresponds to a valid forward lookup, but this verification step is missing or incomplete. The vulnerability enables attackers to present false hostnames that pass the validation checks, potentially allowing them to gain access to restricted resources or manipulate audit trails.
The operational impact of this vulnerability extends beyond simple access control bypasses, as it fundamentally compromises the integrity of client identification within the FTP environment. Attackers can exploit this flaw to circumvent hostname-based access controls that are commonly implemented to restrict access to specific network segments or client groups. This weakness undermines the logging mechanism by allowing incorrect hostnames to be recorded in audit trails, potentially masking malicious activities or creating false security indicators. The vulnerability is particularly concerning because it operates at the authentication and authorization level, potentially allowing unauthorized access to sensitive files and resources that should be protected by hostname-based ACLs.
This vulnerability aligns with CWE-200, which addresses improper output sanitization, and relates to the broader category of insecure hostname resolution practices that have been documented in various network services. The flaw demonstrates a classic case of insufficient input validation where the system assumes that reverse DNS lookup results are trustworthy without proper verification. From an ATT&CK framework perspective, this vulnerability maps to technique T1078 which covers valid accounts and privilege escalation through manipulation of authentication mechanisms, as well as T1566 which involves social engineering through manipulation of network services. Organizations implementing ProFTPD services that rely on hostname-based access controls are particularly vulnerable to this type of attack, as the flaw essentially allows attackers to spoof their hostnames and bypass security restrictions.
Mitigation strategies for CVE-2001-1500 require immediate implementation of proper hostname verification mechanisms within the ProFTPD configuration. System administrators should ensure that reverse DNS lookups are validated through forward resolution checks before accepting hostname information for access control decisions. The recommended approach involves configuring the FTP daemon to perform both forward and reverse DNS resolution for all client connections and comparing the results to ensure consistency. Additionally, organizations should consider implementing more robust authentication mechanisms that do not rely solely on hostname-based access controls, particularly in environments where security is paramount. Updates to ProFTPD to versions that address this specific vulnerability should be prioritized, as the flaw represents a fundamental weakness in the software's security architecture that could be exploited for various malicious purposes including unauthorized file access, data exfiltration, and audit trail manipulation.