CVE-2016-2554 in PHP
Summary
by MITRE
Stack-based buffer overflow in ext/phar/tar.c in PHP before 5.5.32, 5.6.x before 5.6.18, and 7.x before 7.0.3 allows remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact via a crafted TAR archive.
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Analysis
by VulDB Data Team • 08/19/2022
The vulnerability identified as CVE-2016-2554 represents a critical stack-based buffer overflow flaw located within the phar extension of PHP, specifically in the tar.c file component. This issue affects multiple PHP versions including those before 5.5.32, 5.6.x before 5.6.18, and 7.x before 7.0.3, making it a widespread concern across the PHP ecosystem. The vulnerability stems from inadequate input validation when processing TAR archive files through PHP's phar extension, which is commonly used for handling PHP archive files and can be leveraged for various file operations.
The technical flaw manifests when PHP processes a specially crafted TAR archive that contains malformed or oversized data within its headers or file entries. The buffer overflow occurs because the application fails to properly validate the size of data being read from the TAR archive before copying it into fixed-size stack buffers. This allows an attacker to overwrite adjacent memory locations, potentially leading to application crashes or more severe consequences depending on the execution context. The vulnerability specifically targets the phar extension's TAR parsing functionality, which is part of PHP's broader archive handling capabilities that support multiple archive formats including TAR, ZIP, and PHAR.
From an operational perspective, this vulnerability presents significant risks to web applications that utilize PHP's phar extension for handling user-uploaded archives or external archive processing. Remote attackers can exploit this flaw by uploading or providing a maliciously crafted TAR archive that, when processed by PHP, triggers the buffer overflow condition. The impact ranges from denial of service attacks that crash the web application to potential code execution scenarios in certain configurations, though the latter requires additional conditions to be met. The vulnerability's classification aligns with CWE-121 Stack-based Buffer Overflow, which is categorized under the broader weakness of insufficient boundary checking in memory management operations.
The attack surface for this vulnerability is considerable given that many web applications and content management systems rely on PHP's phar extension for file handling operations, particularly when dealing with user uploads or automated archive processing. The exploitability factor is enhanced by the fact that TAR archives are commonly used file formats, making them a plausible attack vector through various means including file upload restrictions bypasses or direct archive processing from external sources. Organizations using affected PHP versions should consider implementing immediate mitigations including patching to the latest stable versions, disabling phar extension functionality when not required, or implementing strict input validation for archive processing operations.
This vulnerability demonstrates the importance of proper input validation and memory management in server-side applications, particularly when handling untrusted data from external sources. The remediation strategy should focus on applying the official PHP security patches that address the buffer overflow conditions in the tar.c file. Additionally, organizations should implement security monitoring to detect potential exploitation attempts and consider network-level controls to restrict access to archive processing functions when possible. The vulnerability also highlights the need for comprehensive security testing of third-party libraries and extension components within PHP applications, as the flaw exists in a core extension that many applications depend upon for archive handling capabilities.