CVE-2001-0136 in ProFTPD
Summary
by MITRE
Memory leak in ProFTPd 1.2.0rc2 allows remote attackers to cause a denial of service via a series of USER commands, and possibly SIZE commands if the server has been improperly installed.
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Analysis
by VulDB Data Team • 10/08/2025
The vulnerability identified as CVE-2001-0136 represents a critical memory leak flaw in ProFTPd version 1.2.0rc2 that exposes the service to remote denial of service attacks. This issue stems from improper memory management within the ftpd daemon implementation where repeated USER command processing fails to properly release allocated memory resources. The vulnerability manifests when remote attackers continuously submit USER commands to the ftpd service, causing progressive memory consumption that eventually leads to system resource exhaustion and service unavailability.
The technical root cause of this memory leak can be traced to CWE-401, which specifically addresses improper handling of memory allocation and deallocation in software systems. When the ProFTPd server processes USER commands, it allocates memory structures to store user authentication information and session data. However, the implementation fails to properly free this memory after each command execution, creating a gradual accumulation of unreleased memory blocks. This memory leak becomes particularly problematic when attackers systematically submit multiple USER commands in sequence, as each iteration consumes additional memory without corresponding cleanup operations.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire server infrastructure. When the memory leak reaches critical thresholds, the ProFTPd service becomes unresponsive and may crash entirely, requiring manual intervention for restart. Additionally, the vulnerability may be exacerbated by improper server installations where the SIZE command processing also exhibits similar memory management flaws, expanding the attack surface for potential exploitation. The cumulative effect of this vulnerability can lead to sustained denial of service conditions that may persist until system reboot or manual service restart.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks. The attack vector operates over standard ftpd protocol connections and requires minimal privileges to execute, making it particularly dangerous for public-facing servers. The memory leak behavior creates a predictable pattern that attackers can exploit systematically, and the vulnerability affects the availability aspect of the CIA triad by compromising system accessibility. Organizations running ProFTPd servers should prioritize immediate patching of this vulnerability as it represents a fundamental memory management failure that could be exploited by automated scanning tools to identify vulnerable systems.
The mitigation strategy for this vulnerability requires immediate deployment of the official ProFTPd patch that addresses the memory allocation and deallocation routines in the USER command processing. System administrators should also implement monitoring solutions to detect unusual memory consumption patterns in ftpd processes, enabling early detection of potential exploitation attempts. Network segmentation and access control measures can provide additional defense layers by limiting exposure of vulnerable ftpd services to untrusted networks. Furthermore, regular security assessments should verify proper installation and configuration of ftpd services to prevent the cascading effects that may occur when servers are improperly configured, which could exacerbate the memory leak conditions and increase attack surface.