CVE-2004-2259 in vsftpd
Summary
by MITRE
vsftpd before 1.2.2, when under heavy load, allows attackers to cause a denial of service (crash) via a SIGCHLD signal during a malloc or free call, which is not re-entrant.
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Analysis
by VulDB Data Team • 06/25/2018
The vulnerability identified as CVE-2004-2259 affects vsftpd versions prior to 1.2.2 and represents a critical denial of service flaw that emerges under heavy system load conditions. This vulnerability specifically targets the signal handling mechanisms within the ftp daemon implementation, creating a scenario where malicious actors can exploit the software's inability to properly manage concurrent processes during memory allocation and deallocation operations. The issue manifests when the vsftpd process receives a SIGCHLD signal while executing malloc or free system calls, causing the application to crash and resulting in complete service disruption for legitimate users attempting to access ftp resources.
The technical root cause of this vulnerability lies in the non-reentrant nature of memory management functions within the vsftpd codebase. When multiple processes or threads attempt to allocate or deallocate memory simultaneously under high load conditions, the signal handler for SIGCHLD interferes with these critical memory operations. This creates a race condition where the signal handling routine attempts to execute while memory allocation is in progress, leading to undefined behavior and ultimately system crash. The vulnerability is particularly dangerous because it leverages the fundamental signal handling architecture of unix-like systems, where SIGCHLD signals are automatically generated when child processes terminate, making it difficult to predict or prevent the timing of such interference.
The operational impact of CVE-2004-2259 extends beyond simple service disruption, as it can be exploited by attackers to systematically degrade system availability and compromise the reliability of ftp services. This vulnerability aligns with CWE-362, which describes "Concurrent Execution using Shared Resource with Improper Synchronization," and represents a classic example of how signal handling can introduce security flaws in multi-threaded or multi-process applications. Under heavy load conditions, the vulnerability becomes more pronounced and easier to exploit, making it particularly dangerous for publicly accessible ftp servers that may experience varying levels of traffic. The flaw affects systems where vsftpd is deployed as a primary file transfer service, potentially impacting organizations that rely on ftp protocols for data exchange, software distribution, or backup operations.
Mitigation strategies for this vulnerability require immediate patching of affected vsftpd installations to version 1.2.2 or later, which includes proper signal handling mechanisms that prevent interference with memory management operations. System administrators should implement monitoring solutions to detect unusual signal activity patterns and consider implementing rate limiting or load balancing mechanisms to reduce the likelihood of triggering the vulnerability. The remediation process should also include reviewing and updating signal handling routines in other similar ftp implementations and ensuring that all memory allocation functions are properly synchronized. Organizations should also consider implementing intrusion detection systems that can identify exploitation attempts targeting this specific vulnerability pattern. This vulnerability demonstrates the importance of proper signal handling design in server applications and serves as a reminder of the critical need to address concurrency issues in network services, particularly those that handle multiple simultaneous connections and resource management operations.