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Executive Summary
CVE-2023-3824, a buffer overflow vulnerability in PHP’s PHAR extension, also impacts PHP 7 installations though official advisories only mention PHP 8+ versions. This vulnerability is particularly concerning as a Proof of Concept (PoC) exploit is publicly available on GitHub, significantly lowering the barrier for potential attackers.
Risk scores for this vulnerability:
9.8 CVSS 3.x from NVD
9.4 CVSS 3.x from PHP Group
The Vulnerability Explained
CVE-2023-3824 is a buffer overflow vulnerability in PHP’s PHAR extension that occurs due to improper bounds checking within the phar_dir_read() function. When a PHP application opens a specially crafted .phar archive, this vulnerability can be triggered, leading to:
- Stack buffer overflow
- Memory corruption
- Information leakage from the stack
- Potential for remote code execution (RCE)
- Denial of service conditions
The severity of this vulnerability is heightened by the fact that opening a malicious PHAR file is the only requirement to trigger the exploit, making it relatively easy to weaponize against vulnerable systems.
PHP 7: Vulnerable and Unpatched
The official advisory for CVE-2023-3824 states that it affects:
- PHP 8.0.* before 8.0.30
- PHP 8.1.* before 8.1.22
- PHP 8.2.* before 8.2.8
However, our security research has confirmed that PHP 7 series installations are also vulnerable to this same issue. This represents a significant security gap, as:
- PHP 7 has reached End-of-Life (EOL) status
- No official patches are available from PHP maintainers
- A public exploit makes this vulnerability particularly dangerous for unpatched systems
Technical Details and Public Exploit Risk
What makes CVE-2023-3824 especially concerning is the availability of a public Proof of Concept on GitHub, significantly lowering the barrier to exploitation. The vulnerability can be exploited through a straightforward two-step process:
- First, an attacker can craft a malicious PHAR file with specifically manipulated directory entry names that approach or exceed PHP’s maximum path length (PHP_MAXPATHLEN)
- Then, when this crafted file is accessed through PHP’s PHAR stream wrapper, the vulnerability is triggered
The technical issue occurs because the phar_dir_read() function fails to properly validate input lengths before writing to a stack buffer. When the vulnerable PHP installation processes a malicious PHAR file with carefully crafted directory entries, insufficient length checking leads to a stack buffer overflow. This can cause memory corruption and potentially allow attackers to:
- Read sensitive data from memory
- Execute arbitrary code on the affected system
- Cause application crashes and service disruptions
Comparison with CVE-2023-0568
This vulnerability shares similarities with CVE-2023-0568 (discussed in a previous article), as both involve buffer overflow issues that could lead to memory corruption. However, CVE-2023-3824 poses a more immediate threat due to:
- The public availability of a working exploit
- Its potential for remote code execution
- The relatively simple attack vector (processing a PHAR file)
Our Solution: Endless Lifecycle Support for PHP 7
As with CVE-2023-0568, we understand that many organizations continue to run PHP 7 applications due to compatibility requirements or resource constraints. Our Endless Lifecycle Support (ELS) service address this gap by providing:
- Custom Security Patches: We’ve developed patches for PHP 7 that address CVE-2023-3824 and other known vulnerabilities
- Updated PHP 7 Packages: Available for both Windows and Linux environments
- Proactive Security Monitoring: Continuous identification of vulnerabilities that affect PHP 7, even when not officially acknowledged
Recommended Actions
If your organization is running PHP 7, we strongly recommend the following immediate actions:
- Apply Our Security Patches: Install our patched PHP 7 packages to protect against this vulnerability
- Disable PHAR Support If Not Needed: If your applications don’t require PHAR functionality, consider disabling it as a temporary mitigation
- Implement Additional Security Controls: Consider web application firewalls or other security measures that can detect and block exploitation attempts
Final Thoughts
The discovery of CVE-2023-3824 affecting PHP 7, combined with the public availability of exploit code, creates a perfect storm for organizations running EOL PHP versions. This vulnerability exemplifies why extended security support is crucial for organizations that cannot immediately upgrade to newer PHP versions.
Our Endless Lifecycle Support for PHP 7, for Windows and Linux, provides the security updates necessary to protect your systems while you plan and execute your migration strategy at a pace that works for your business needs.
