CVE-2015-4643 in PHP
Summary
by MITRE
Integer overflow in the ftp_genlist function in ext/ftp/ftp.c in PHP before 5.4.42, 5.5.x before 5.5.26, and 5.6.x before 5.6.10 allows remote FTP servers to execute arbitrary code via a long reply to a LIST command, leading to a heap-based buffer overflow. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-4022.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/21/2022
The vulnerability identified as CVE-2015-4643 represents a critical integer overflow flaw within the PHP FTP extension that has significant implications for web application security. This vulnerability specifically affects PHP versions prior to 5.4.42, 5.5.x prior to 5.5.26, and 5.6.x prior to 5.6.10, making it a widespread concern across multiple PHP version lines. The flaw resides in the ftp_genlist function located in ext/ftp/ftp.c, which handles FTP server responses during file listing operations. The vulnerability stems from inadequate input validation when processing FTP LIST command responses, creating a scenario where remote FTP servers can manipulate the system through carefully crafted long replies.
The technical implementation of this vulnerability involves an integer overflow condition that occurs when the ftp_genlist function processes FTP server responses. When a remote FTP server sends an unusually long reply to a LIST command, the function fails to properly validate the length of the response before attempting to allocate memory for processing. This incomplete validation leads to an integer overflow that subsequently causes a heap-based buffer overflow. The buffer overflow occurs because the system attempts to allocate insufficient memory for the oversized response, allowing malicious data to overwrite adjacent memory regions. This memory corruption creates opportunities for attackers to execute arbitrary code on systems running vulnerable PHP versions, effectively bypassing normal security boundaries.
From an operational perspective, this vulnerability presents a severe risk to web applications that utilize PHP's FTP functionality, particularly those that connect to untrusted FTP servers or process FTP responses from external sources. The attack vector requires a remote FTP server to be compromised or maliciously configured to send oversized LIST command responses, which then triggers the overflow condition. Security researchers have noted that this vulnerability is particularly dangerous because it can be exploited without requiring authentication or special privileges on the target system. The exploitation process typically involves crafting a specific FTP response that causes the integer overflow, leading to memory corruption that can be leveraged for code execution. This makes the vulnerability especially concerning for applications that handle user-provided FTP server information or that aggregate data from multiple FTP sources.
The vulnerability's classification aligns with CWE-190, which addresses integer overflow conditions, and represents a specific instance of heap-based buffer overflow exploitation. From an attack framework perspective, this vulnerability maps to multiple ATT&CK techniques including T1059 for command and script injection, and T1203 for exploitation of remote services. The incomplete fix for CVE-2015-4022, which this vulnerability is noted as being related to, demonstrates how security patches can sometimes introduce new weaknesses if not thoroughly validated. Organizations should prioritize immediate patching of affected PHP versions, as the vulnerability enables remote code execution capabilities that can lead to complete system compromise. Additionally, network segmentation and firewall rules should be implemented to restrict FTP access from untrusted sources, while monitoring systems should be configured to detect unusual FTP LIST command responses that might indicate exploitation attempts. The remediation strategy must also include comprehensive testing of patched environments to ensure that the fix does not introduce regressions in legitimate FTP functionality, particularly in applications that rely on processing large FTP directory listings.