CVE-2019-18217 in ProFTPD
Summary
by MITRE
ProFTPD before 1.3.6b and 1.3.7rc before 1.3.7rc2 allows remote unauthenticated denial-of-service due to incorrect handling of overly long commands because main.c in a child process enters an infinite loop.
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Analysis
by VulDB Data Team • 01/17/2024
The vulnerability identified as CVE-2019-18217 represents a critical denial-of-service flaw affecting ProFTPD versions prior to 1.3.6b and 1.3.7rc2. This weakness stems from improper handling of excessively long command inputs within the main.c source file, specifically within child process execution contexts. The flaw manifests when the ftpd daemon processes malformed or overly lengthy commands without adequate input validation or length checking mechanisms, creating a condition where the software enters an infinite loop during command processing. This behavior fundamentally disrupts the normal operation of the ftpd service, rendering it unresponsive to legitimate client requests and effectively preventing authorized users from accessing the file transfer protocol service.
The technical root cause of this vulnerability lies in the insufficient input sanitization and boundary checking within the ProFTPD daemon's command parsing logic. When a remote attacker sends a command containing an abnormally long string of characters, the main.c module fails to properly terminate command processing or implement appropriate loop termination conditions. The child process responsible for handling these commands becomes trapped in an infinite loop, consuming system resources and preventing the daemon from processing subsequent legitimate requests. This condition persists until the system administrator manually intervenes to restart the service or the process eventually exhausts available resources, making the system unavailable to all users.
From an operational perspective, this vulnerability presents significant risks to organizations relying on ProFTPD for file transfer operations. The denial-of-service attack can be executed remotely without requiring authentication credentials, making it particularly dangerous as any external party can exploit this weakness. The infinite loop condition causes the ftpd service to become unresponsive, which can result in complete service disruption for legitimate users attempting to access files or perform transfers. Network administrators may experience extended downtime as they must manually restart the service or investigate the root cause, potentially disrupting business operations and affecting critical file sharing processes. The vulnerability's impact is amplified in environments where continuous availability of file transfer services is essential for business operations.
Security practitioners should implement immediate mitigations including updating ProFTPD installations to versions 1.3.6b or 1.3.7rc2, which contain the necessary patches to address the command handling flaw. Organizations should also consider implementing network-level protections such as rate limiting and connection monitoring to detect and prevent exploitation attempts. The vulnerability aligns with CWE-835, which describes infinite loops or infinite recursion conditions, and represents a classic example of inadequate input validation that can lead to resource exhaustion. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, specifically targeting service availability through resource exhaustion techniques, making it a significant concern for organizations maintaining robust cybersecurity postures. Additionally, implementing proper input length validation and implementing timeout mechanisms within the ftpd daemon configuration can provide additional defense-in-depth measures against similar exploitation attempts.