CVE-2023-0568: PHP Buffer Overflow Vulnerability

CVE-2023-0568 Overview

CVE-2023-0568 is a critical off-by-one buffer overflow vulnerability affecting PHP's core path resolution functionality. The vulnerability occurs when the path resolution function allocates a buffer that is one byte too small. When resolving paths with lengths close to the system's MAXPATHLEN setting, this miscalculation can cause the byte immediately following the allocated buffer to be overwritten with a NUL value, potentially leading to unauthorized data access or modification.

Critical Impact

Successful exploitation of this vulnerability could allow attackers to access or modify unauthorized data through memory corruption, potentially compromising the integrity and confidentiality of PHP-based applications and systems.

Affected Products

• PHP 8.0.X before 8.0.28
• PHP 8.1.X before 8.1.16
• PHP 8.2.X before 8.2.3

Discovery Timeline

• 2023-02-16 - CVE-2023-0568 published to NVD
• 2025-02-13 - Last updated in NVD database

Technical Details for CVE-2023-0568

Vulnerability Analysis

This vulnerability is classified under CWE-131 (Incorrect Calculation of Buffer Size) and CWE-770 (Allocation of Resources Without Limits or Throttling). The flaw resides in PHP's internal path resolution mechanism, which is responsible for converting relative paths to absolute paths and normalizing path components.

When processing file paths that approach the system's MAXPATHLEN limit, the buffer allocation routine fails to account for the NUL terminator byte. This off-by-one error creates a condition where the path resolution function writes beyond the allocated buffer boundary, specifically overwriting the adjacent byte with a NUL (0x00) value.

The vulnerability is exploitable over the network without requiring authentication or user interaction, though exploitation complexity is considered high due to the specific path length requirements that must be met. Successful exploitation could result in significant impacts to confidentiality and integrity.

Root Cause

The root cause is an incorrect buffer size calculation in PHP's core path resolution function. The function calculates the required buffer size but fails to include space for the null terminator character, resulting in a buffer that is exactly one byte smaller than required. When the resolved path length approaches MAXPATHLEN, this miscalculation causes an out-of-bounds write condition.

Attack Vector

The attack vector involves crafting file path inputs with lengths close to the system's maximum path length limit (MAXPATHLEN). An attacker would need to:

1. Identify PHP applications that perform path resolution operations on user-controllable input
2. Craft path strings that, when resolved, approach the MAXPATHLEN boundary
3. Trigger the path resolution function to cause the off-by-one overflow
4. Leverage the memory corruption to access or modify unauthorized data

The exploitation requires precise control over path lengths and understanding of the target system's memory layout, which contributes to the high attack complexity rating.

Detection Methods for CVE-2023-0568

Indicators of Compromise

• Unusual PHP process crashes or segmentation faults related to file operations
• Error logs indicating path resolution failures with unusually long file paths
• Anomalous memory access patterns in PHP processes handling file path operations
• Unexplained data modifications in applications processing user-supplied file paths

Detection Strategies

• Monitor PHP error logs for segmentation faults and memory-related errors during path operations
• Implement application-level logging for file path operations that approach system path length limits
• Deploy runtime application self-protection (RASP) solutions to detect buffer overflow attempts
• Use SentinelOne's behavioral AI to identify anomalous memory access patterns in PHP processes

Monitoring Recommendations

• Configure alerting for PHP process crashes that may indicate exploitation attempts
• Monitor file system activity for operations involving exceptionally long path names
• Implement log correlation to identify patterns of path manipulation across multiple requests
• Enable detailed PHP error logging to capture path resolution failures

How to Mitigate CVE-2023-0568

Immediate Actions Required

• Upgrade PHP 8.0.X installations to version 8.0.28 or later immediately
• Upgrade PHP 8.1.X installations to version 8.1.16 or later immediately
• Upgrade PHP 8.2.X installations to version 8.2.3 or later immediately
• Conduct an inventory of all PHP installations to ensure complete coverage

Patch Information

The PHP development team has addressed this vulnerability in the following releases:

For detailed information about the bug and its resolution, refer to the PHP Bug Report #81746. Additional vendor security information is available in the NetApp Security Advisory ntap-20230517-0001.

Workarounds

• Implement input validation to reject file paths exceeding reasonable length thresholds
• Configure web application firewalls (WAF) to filter requests containing excessively long path components
• Apply operating system-level path length restrictions where supported
• Use containerization to isolate PHP applications and limit potential impact of exploitation

# Configuration example - Validate path lengths in application
# Add to PHP configuration or application bootstrap
# Limit maximum path length processing (example using open_basedir)
php_admin_value[open_basedir] = /var/www/html:/tmp
php_admin_value[max_execution_time] = 30