CVE-2015-4022 in PHP
Summary
by MITRE
Integer overflow in the ftp_genlist function in ext/ftp/ftp.c in PHP before 5.4.41, 5.5.x before 5.5.25, and 5.6.x before 5.6.9 allows remote FTP servers to execute arbitrary code via a long reply to a LIST command, leading to a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 05/19/2022
The vulnerability identified as CVE-2015-4022 represents a critical integer overflow flaw within PHP's File Transfer Protocol implementation that has significant implications for web application security. This vulnerability exists in the ftp_genlist function located in the ext/ftp/ftp.c source file of PHP, affecting multiple major versions including PHP 5.4.40 and earlier, 5.5.24 and earlier, and 5.6.8 and earlier. The flaw specifically manifests when PHP processes FTP LIST command responses from remote servers, creating a dangerous condition that can be exploited by malicious FTP servers to execute arbitrary code on systems running vulnerable PHP versions.
The technical mechanism behind this vulnerability involves an integer overflow condition that occurs during the processing of FTP directory listings. When a remote FTP server responds to a LIST command with an unusually long reply, the ftp_genlist function fails to properly validate the length of the response data before attempting to allocate memory for processing. This integer overflow results in an incorrect calculation of buffer size needed for storing the FTP directory listing data, ultimately leading to a heap-based buffer overflow condition. The overflow occurs because the system attempts to allocate a buffer that is smaller than required, but the subsequent memory operations write data beyond the allocated boundaries, creating exploitable memory corruption.
The operational impact of CVE-2015-4022 is severe and far-reaching, as it allows remote attackers to execute arbitrary code on systems running vulnerable PHP versions. This vulnerability can be exploited in various attack scenarios including web application compromise, server takeover, and privilege escalation. The attack vector requires a malicious FTP server to be accessible to the vulnerable PHP application, which means that any web application that utilizes PHP's FTP functions and connects to untrusted FTP servers could be at risk. The vulnerability is particularly dangerous in environments where PHP applications handle user-provided FTP server information or when applications connect to public FTP servers that may be compromised. This flaw can lead to complete system compromise, data theft, and unauthorized access to sensitive information stored on affected systems.
The vulnerability maps directly to CWE-190, which describes integer overflow conditions, and aligns with ATT&CK technique T1190, which covers exploitation of remote services. Organizations should immediately implement mitigations including updating to patched PHP versions, specifically PHP 5.4.41, 5.5.25, or 5.6.9, and later releases. Additional protective measures include implementing network segmentation to limit access to FTP servers, using secure FTP protocols where possible, and monitoring for suspicious FTP activity. System administrators should also consider disabling FTP functionality in PHP applications when it is not strictly required, and implementing proper input validation for any FTP server connections that must remain active. The remediation process should include thorough testing of patched versions to ensure that no regressions occur in existing FTP functionality while addressing the critical buffer overflow vulnerability.