CVE-2025-14178: PHP Buffer Overflow Vulnerability

CVE-2025-14178 Overview

CVE-2025-14178 is a heap buffer overflow vulnerability affecting multiple versions of PHP. The vulnerability exists in the array_merge() function where a heap buffer overflow occurs when the total element count of packed arrays exceeds 32-bit limits or HT_MAX_SIZE. This is caused by an integer overflow in the precomputation of element counts using zend_hash_num_elements(). Successful exploitation may lead to memory corruption or crashes, affecting the integrity and availability of PHP-powered web servers and applications.

Critical Impact

This vulnerability can result in memory corruption or denial of service conditions on PHP servers, potentially affecting web application availability and data integrity for any system running vulnerable PHP versions.

Affected Products

• PHP 8.1.* before 8.1.34
• PHP 8.2.* before 8.2.30
• PHP 8.3.* before 8.3.29
• PHP 8.4.* before 8.4.16
• PHP 8.5.* before 8.5.1

Discovery Timeline

• 2025-12-27 - CVE-2025-14178 published to NVD
• 2026-01-24 - Last updated in NVD database

Technical Details for CVE-2025-14178

Vulnerability Analysis

This vulnerability stems from improper handling of large array sizes within PHP's array_merge() function. When merging multiple packed arrays, PHP precomputes the total number of elements that will be present in the resulting merged array using the zend_hash_num_elements() function. However, when the combined element count approaches or exceeds the maximum value representable by a 32-bit integer or the internal HT_MAX_SIZE constant, an integer overflow condition occurs.

The integer overflow causes the allocated memory buffer to be significantly smaller than required to hold all the merged elements. As the merge operation proceeds and attempts to write beyond the undersized buffer, a heap buffer overflow condition is triggered. This can corrupt adjacent heap memory structures, leading to unpredictable behavior including crashes, memory corruption, and potential exploitation scenarios.

Root Cause

The root cause is an integer overflow vulnerability (CWE-190) in the element count calculation logic within array_merge(). The function uses zend_hash_num_elements() to determine the size of the destination array but fails to properly validate that the cumulative count remains within safe bounds before memory allocation. When the sum of elements from multiple input arrays wraps around due to integer overflow, an insufficient buffer is allocated, resulting in subsequent heap memory corruption during the merge operation.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Sending specially crafted HTTP requests to a PHP application that processes user-controlled array data
2. Providing multiple large arrays to an endpoint that uses array_merge() to combine them
3. Triggering the integer overflow condition by ensuring the total element count exceeds safe limits
4. Causing the heap buffer overflow to corrupt memory, potentially leading to denial of service or, in some scenarios, arbitrary code execution

The vulnerability is particularly concerning for web applications that accept and merge array data from untrusted sources, such as form submissions, API endpoints, or file uploads containing serialized array data.

Detection Methods for CVE-2025-14178

Indicators of Compromise

• Unexpected PHP process crashes or segmentation faults in application logs
• Memory corruption errors or heap-related crashes in PHP error logs
• Abnormal memory usage patterns in PHP-FPM or Apache mod_php processes
• Application behavior anomalies following processing of large array data

Detection Strategies

• Monitor PHP error logs for segmentation faults, memory allocation failures, or unexpected crashes related to array operations
• Implement web application firewall rules to detect and block requests with unusually large or numerous array parameters
• Use runtime application self-protection (RASP) solutions to monitor for heap corruption attempts
• Deploy SentinelOne Singularity to detect memory corruption exploitation attempts and anomalous process behavior

Monitoring Recommendations

• Enable verbose PHP error logging and centralize logs for analysis
• Implement monitoring alerts for PHP process crashes and restarts
• Monitor system memory usage for abnormal spikes during request processing
• Track application response times for degradation that may indicate exploitation attempts

How to Mitigate CVE-2025-14178

Immediate Actions Required

• Upgrade PHP to a patched version immediately: 8.1.34, 8.2.30, 8.3.29, 8.4.16, or 8.5.1
• Review application code for uses of array_merge() with user-controlled input and implement input validation
• Deploy web application firewall rules to limit array sizes in incoming requests
• Consider implementing rate limiting on endpoints that process array data

Patch Information

PHP has released security patches addressing this vulnerability across all affected version branches. Organizations should upgrade to the following minimum versions:

For detailed patch information, refer to the PHP Security Advisory on GitHub. Debian users should also review the Debian LTS Security Announcement for distribution-specific guidance.

Workarounds

• Implement strict input validation to limit the size and number of arrays accepted from user input before passing to array_merge()
• Use PHP's memory_limit configuration directive to constrain maximum memory allocation per request
• Deploy a web application firewall to filter requests containing excessively large array parameters
• Consider implementing application-level checks to validate total element counts before merging arrays

# PHP configuration hardening example
# Add to php.ini or php-fpm pool configuration

# Limit maximum memory per request to reduce impact of exploitation
memory_limit = 128M

# Limit maximum input variables (helps constrain array sizes)
max_input_vars = 1000

# Set maximum POST data size
post_max_size = 8M

# Limit input nesting depth
max_input_nesting_level = 64