CVE-2016-5399 in PHP
Summary
by MITRE
The bzread function in ext/bz2/bz2.c in PHP before 5.5.38, 5.6.x before 5.6.24, and 7.x before 7.0.9 allows remote attackers to cause a denial of service (out-of-bounds write) or execute arbitrary code via a crafted bz2 archive.
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability identified as CVE-2016-5399 represents a critical security flaw within the PHP bz2 extension that affects multiple PHP versions including 5.5.37 and earlier, 5.6.23 and earlier, and 7.0.8 and earlier. This issue stems from improper handling of maliciously crafted bzip2 archives within the bzread function located in ext/bz2/bz2.c. The flaw manifests as an out-of-bounds write condition that can be exploited by remote attackers to either cause a denial of service or achieve arbitrary code execution on vulnerable systems. The vulnerability falls under the category of memory corruption issues and is classified as a buffer overflow condition that occurs during the decompression process of bzip2 files.
The technical implementation of this vulnerability occurs when PHP processes a specially crafted bzip2 archive through the bzread function. During the decompression operation, the application fails to properly validate the structure and boundaries of the compressed data, leading to memory corruption. When the decompression algorithm encounters malformed data within the bzip2 archive, it attempts to write data beyond the allocated memory boundaries, resulting in unpredictable behavior. This out-of-bounds write condition can be manipulated by attackers to overwrite critical memory locations, potentially leading to code execution or system instability. The vulnerability demonstrates characteristics consistent with CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which addresses out-of-bounds write vulnerabilities.
The operational impact of CVE-2016-5399 extends beyond simple denial of service scenarios, as it provides potential for remote code execution on affected systems. Attackers can exploit this vulnerability by uploading or delivering a malicious bzip2 archive to a PHP application that processes user-supplied data through the bz2 extension. This attack vector is particularly concerning in web environments where PHP applications handle file uploads or process external data sources. The vulnerability affects systems that utilize the bz2 extension for decompressing data, including web applications, content management systems, and any PHP-based services that accept bzip2 formatted input. The exploitability of this vulnerability is enhanced in environments where PHP applications perform automatic decompression of user-provided files without proper validation or sanitization, creating a significant risk for web applications that process external data.
Mitigation strategies for CVE-2016-5399 focus primarily on patching affected PHP installations to versions that contain the necessary security fixes. System administrators should immediately upgrade to PHP 5.5.38, 5.6.24, or 7.0.9 and later versions where the vulnerability has been addressed. Additionally, implementing proper input validation and sanitization measures can help reduce the attack surface by preventing the processing of untrusted bzip2 data. Organizations should also consider disabling the bz2 extension entirely if it is not required for critical applications, as this eliminates the attack vector. Network-based mitigations such as intrusion detection systems can help identify potential exploitation attempts, while application-level restrictions on file upload functionality can provide additional layers of defense. The vulnerability aligns with ATT&CK technique T1059.007, which covers command and scripting interpreter usage, and T1499.004, related to network denial of service, demonstrating the multi-faceted nature of the threat posed by this vulnerability. Regular security assessments and vulnerability scanning should be conducted to ensure that systems remain protected against similar memory corruption vulnerabilities in the PHP ecosystem.