CVE-2025-14178 is a heap buffer overflow vulnerability identified in multiple PHP versions (8.1.* before 8.1.34, 8.2.* before 8.2.30, 8.3.* before 8.3.29, 8.4.* before 8.4.16, and 8.5.* before 8.5.1). The flaw arises in the array_merge() function when it processes packed arrays whose combined element count exceeds the 32-bit integer limit or the internal HT_MAX_SIZE threshold. This condition triggers an integer overflow during the precomputation of element counts via zend_hash_num_elements(), leading to an incorrect allocation size for the heap buffer. Consequently, this results in a heap buffer overflow, causing memory corruption. The corrupted memory state can lead to application crashes or potentially unpredictable behavior affecting the integrity and availability of PHP applications. The vulnerability does not require any privileges or user interaction but has a high attack complexity due to the need to craft arrays exceeding specific size limits. There are no known exploits in the wild at the time of publication. The CVSS v3.1 base score is 6.5, reflecting a medium severity with network attack vector, no privileges required, no user interaction, and impact primarily on availability and integrity. This vulnerability is relevant for any PHP-based web applications or services running affected versions, especially those exposed to untrusted input that could trigger large array merges.

For European organizations, this vulnerability poses a risk primarily to the availability and integrity of PHP-based web services and applications. Exploitation could lead to denial of service through application crashes or memory corruption, disrupting business operations and potentially causing downtime. While no direct confidentiality impact is indicated, the instability could be leveraged as part of a broader attack chain. Organizations running vulnerable PHP versions on public-facing websites, APIs, or internal tools are at risk, especially those handling large or complex data merges. The medium severity and high attack complexity suggest targeted exploitation rather than widespread automated attacks. However, the widespread use of PHP in Europe across government, finance, e-commerce, and critical infrastructure sectors means the potential impact is significant. Disruptions could affect customer trust, regulatory compliance (e.g., GDPR), and operational continuity. The lack of known exploits currently provides a window for proactive mitigation.

1. Upgrade PHP to the fixed versions as soon as they become available: 8.1.34, 8.2.30, 8.3.29, 8.4.16, or 8.5.1 or later. 2. In the interim, audit and limit the use of array_merge() with large or untrusted input arrays, especially those that could exceed 32-bit element counts or HT_MAX_SIZE. 3. Implement input validation and size checks on arrays before merging to prevent triggering the integer overflow condition. 4. Monitor application logs and system metrics for signs of memory corruption, crashes, or abnormal terminations related to PHP processes. 5. Employ web application firewalls (WAFs) with rules to detect and block suspicious payloads that attempt to exploit large array merges. 6. Conduct code reviews and security testing focusing on array handling in PHP applications. 7. Maintain an incident response plan to quickly address potential denial of service incidents. 8. Keep PHP and all dependencies regularly updated to minimize exposure to known vulnerabilities.