CVE-2019-20176 in Pure-FTPd
Summary
by MITRE • 01/25/2023
In Pure-FTPd 1.0.49, a stack exhaustion issue was discovered in the listdir function in ls.c.
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Analysis
by VulDB Data Team • 03/19/2024
The vulnerability identified as CVE-2019-20176 represents a critical stack exhaustion flaw within Pure-FTPd version 1.0.49, specifically affecting the listdir function implementation in the ls.c source file. This issue arises from inadequate stack memory management during directory listing operations, creating a potential avenue for denial of service attacks that can compromise the stability and availability of the FTP server.
The technical root cause of this vulnerability stems from the improper handling of recursive directory traversal within the listdir function, where the stack memory allocation does not adequately account for deep directory structures or maliciously crafted directory hierarchies. When the FTP server processes directory listings containing excessive nesting levels or specially constructed file paths, the function's recursive calls consume stack space without proper bounds checking or stack overflow protection mechanisms. This flaw aligns with CWE-770, which categorizes inadequate resource management and stack exhaustion issues as critical security weaknesses that can lead to system instability and service disruption.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by remote attackers to systematically consume available stack memory resources on the target system. An attacker can craft specific directory listing requests that trigger deep recursion patterns, causing the server process to exhaust its allocated stack space and resulting in abrupt termination or system instability. This vulnerability directly maps to ATT&CK technique T1499.004, which involves network disruption through resource exhaustion attacks, potentially affecting the availability of critical file transfer services within enterprise environments.
Mitigation strategies for CVE-2019-20176 should prioritize immediate patching of Pure-FTPd installations to versions that address the stack exhaustion issue through proper stack management and recursive call limiting. System administrators should implement monitoring solutions to detect unusual directory listing patterns that might indicate exploitation attempts. Network segmentation and access controls can help limit the attack surface by restricting direct access to FTP services from untrusted networks. Additionally, implementing resource limits and stack size restrictions on FTP server processes can provide defensive measures against potential exploitation attempts. Organizations should also consider deploying intrusion detection systems that can identify anomalous directory traversal patterns and establish regular vulnerability assessment procedures to identify similar issues in other FTP server implementations.