CVE-2023-3824: PHP PHAR Buffer Overflow Vulnerability

CVE-2023-3824 Overview

CVE-2023-3824 is a stack buffer overflow vulnerability in PHP that occurs when loading PHAR (PHP Archive) files. During the parsing of PHAR directory entries, insufficient length validation allows an attacker to trigger a stack buffer overflow condition. This memory corruption vulnerability can potentially lead to remote code execution, allowing attackers to gain unauthorized access to vulnerable systems running affected PHP versions.

Critical Impact
This vulnerability enables potential remote code execution through maliciously crafted PHAR files, putting PHP-based web applications and servers at significant risk of complete compromise.

Affected Products

PHP versions 8.0.* before 8.0.30
PHP versions 8.1.* before 8.1.22
PHP versions 8.2.* before 8.2.8
Fedora 38
Debian Linux 10.0

Discovery Timeline

August 11, 2023 - CVE-2023-3824 published to NVD
February 13, 2025 - Last updated in NVD database

Technical Details for CVE-2023-3824

Vulnerability Analysis

The vulnerability exists in PHP's PHAR file handling functionality, specifically within the code responsible for reading and parsing PHAR directory entries. When a PHP application loads a PHAR file, the interpreter processes the archive's directory structure to enumerate and access the packaged files. The vulnerable code path fails to properly validate the length of directory entry data before copying it into a fixed-size stack buffer.

This insufficient bounds checking allows data to be written beyond the allocated buffer space on the stack. An attacker can exploit this by crafting a malicious PHAR file with specially constructed directory entries containing oversized or malformed length fields. When such a file is processed by a vulnerable PHP instance, the overflow corrupts adjacent stack memory, potentially overwriting return addresses or other critical program data.

The vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which encompasses buffer overflow conditions. Given the network-accessible attack vector requiring no privileges or user interaction, and the potential for complete system compromise through code execution, this vulnerability poses a significant threat to PHP deployments.

Root Cause

The root cause of CVE-2023-3824 is insufficient length validation in PHP's PHAR directory entry parsing code. When reading directory entries from PHAR archives, the code allocates a fixed-size buffer on the stack but does not adequately verify that incoming data will fit within this allocation. The absence of proper bounds checking before memory copy operations allows attacker-controlled data to overflow the buffer and corrupt stack memory.

Attack Vector

The attack vector is network-based, meaning exploitation can occur remotely without requiring local access to the target system. An attacker can deliver a malicious PHAR file through various means:

Direct file upload - If the target application accepts file uploads and processes PHAR files
Deserialization attacks - PHAR files can be triggered through PHP object deserialization via stream wrappers (e.g., phar:// protocol)
Include/require statements - If an attacker can influence file paths used in PHP include statements
Archive processing features - Applications that extract or examine archive contents

The phar:// stream wrapper is particularly dangerous as it can be triggered through various PHP functions that accept file paths, including file_get_contents(), file_exists(), is_dir(), and many others, even when the application doesn't explicitly intend to process PHAR files.

The vulnerability can be exploited without authentication or user interaction, and successful exploitation may result in arbitrary code execution with the privileges of the PHP process, typically the web server user.

Detection Methods for CVE-2023-3824

Indicators of Compromise

Unusual PHAR file uploads or presence of unexpected .phar files on web servers
PHP process crashes or segmentation faults during file operations
Anomalous memory access patterns or stack corruption signatures in crash dumps
Unexpected system calls or process spawning from PHP/web server processes

Detection Strategies

Monitor web application logs for requests containing phar:// stream wrapper references
Implement file integrity monitoring to detect unauthorized PHAR files in web directories
Deploy web application firewalls (WAF) with rules to detect and block PHAR-related attack patterns
Use runtime application self-protection (RASP) solutions to detect buffer overflow attempts

Monitoring Recommendations

Enable PHP error logging and monitor for segmentation faults or memory-related errors
Implement network traffic analysis to identify suspicious file transfers containing PHAR signatures
Configure intrusion detection systems (IDS) to alert on known PHAR exploitation patterns
Review web server access logs for unusual requests targeting file upload or processing endpoints

How to Mitigate CVE-2023-3824

Immediate Actions Required

Upgrade PHP to patched versions: 8.0.30, 8.1.22, or 8.2.8 or later immediately
Audit applications for PHAR file processing functionality and restrict where possible
Disable the phar extension if not required by your applications using php.ini configuration
Implement strict file upload validation and reject PHAR files at the application level

Patch Information

PHP has released security patches addressing this vulnerability in the following versions:

PHP 8.0.30 and later
PHP 8.1.22 and later
PHP 8.2.8 and later

Organizations should update to these versions immediately. For detailed information about the fix, refer to the GitHub Security Advisory.

Distribution-specific updates are available:

Debian users should refer to the Debian LTS Announcement
Fedora users should check the Fedora Package Announcement

Workarounds

Disable PHAR support by adding phar.readonly = 1 and removing phar from enabled extensions in php.ini
Block phar:// stream wrapper usage in web-accessible PHP scripts using stream wrapper restrictions
Implement input validation to reject any user input containing phar:// references
Configure web application firewalls to block requests containing PHAR-related patterns

bash

# Configuration example - Disable PHAR extension in php.ini
# Add or modify the following lines in your php.ini file:

; Disable PHAR writing capability
phar.readonly = 1

; Optionally disable the extension entirely if not needed
; extension=phar  (comment out this line)

# Restart PHP-FPM or web server after changes
sudo systemctl restart php-fpm
sudo systemctl restart nginx  # or apache2