CVE-2016-4343 in PHP
Summary
by MITRE
The phar_make_dirstream function in ext/phar/dirstream.c in PHP before 5.6.18 and 7.x before 7.0.3 mishandles zero-size ././@LongLink files, which allows remote attackers to cause a denial of service (uninitialized pointer dereference) or possibly have unspecified other impact via a crafted TAR archive.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-4343 represents a critical flaw in PHP's phar extension that affects versions prior to 5.6.18 and 7.0.3. This issue resides within the phar_make_dirstream function located in ext/phar/dirstream.c, where the software fails to properly handle zero-size ././@LongLink files during TAR archive processing. The vulnerability manifests when PHP encounters specially crafted TAR archives containing these malformed entries, creating a scenario where the application's memory management becomes compromised.
The technical nature of this vulnerability stems from an uninitialized pointer dereference condition that occurs when the phar extension attempts to process directory streams in TAR archives. When encountering a zero-size ././@LongLink file, the function does not properly validate the file size or handle the edge case, leading to memory access violations. This flaw operates at the core level of PHP's archive handling mechanism, specifically within the phar extension that enables PHP applications to create and manipulate phar files, which are essentially PHP archives that can contain multiple files in a single archive format.
From an operational standpoint, this vulnerability presents a significant denial of service risk that can be exploited remotely by attackers who craft malicious TAR archives. The impact extends beyond simple service disruption as the uninitialized pointer dereference could potentially lead to more severe consequences including arbitrary code execution or information disclosure depending on the execution environment. The vulnerability affects PHP applications that process untrusted TAR archives through the phar extension, making it particularly dangerous in web applications where user uploads or external data processing is common. This flaw aligns with CWE-476 which describes NULL pointer dereferences and represents a classic example of improper input validation in archive processing systems.
The attack surface for this vulnerability is broad given that PHP's phar extension is widely used across web applications for various purposes including application packaging, deployment, and file management. When applications process user-uploaded archives or fetch data from external sources that may contain TAR files, they become susceptible to this attack vector. The vulnerability is particularly concerning in environments where PHP applications handle untrusted input without proper validation or sanitization. According to ATT&CK framework, this represents a privilege escalation technique through resource exhaustion and memory corruption, specifically falling under the category of code injection and denial of service attacks.
Mitigation strategies for CVE-2016-4343 primarily focus on immediate version updates to PHP 5.6.18 or PHP 7.0.3, which contain the necessary patches to properly handle zero-size ././@LongLink files. Organizations should also implement input validation measures that restrict or sanitize archive file processing, particularly for untrusted sources. Network-level protections can include implementing file type restrictions and content inspection to prevent malicious archives from reaching vulnerable PHP applications. Security monitoring should be enhanced to detect unusual patterns in archive processing activities, and regular security assessments should be conducted to ensure that all PHP installations are properly updated and patched against known vulnerabilities. Additionally, developers should avoid processing untrusted archives directly and implement proper error handling and memory management practices within their applications.