CVE-2019-9023 in PHP
Summary
by MITRE
An issue was discovered in PHP before 5.6.40, 7.x before 7.1.26, 7.2.x before 7.2.14, and 7.3.x before 7.3.1. A number of heap-based buffer over-read instances are present in mbstring regular expression functions when supplied with invalid multibyte data. These occur in ext/mbstring/oniguruma/regcomp.c, ext/mbstring/oniguruma/regexec.c, ext/mbstring/oniguruma/regparse.c, ext/mbstring/oniguruma/enc/unicode.c, and ext/mbstring/oniguruma/src/utf32_be.c when a multibyte regular expression pattern contains invalid multibyte sequences.
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Analysis
by VulDB Data Team • 07/19/2023
The vulnerability identified as CVE-2019-9023 represents a critical heap-based buffer over-read issue affecting PHP versions prior to specific patches across multiple release lines. This flaw manifests within the mbstring extension's regular expression processing capabilities, specifically when handling invalid multibyte data sequences. The affected components reside in the oniguruma regular expression engine that PHP utilizes for multibyte string operations, making this a fundamental security concern for applications relying on international text processing. The vulnerability impacts the core functionality of PHP's multibyte string handling mechanisms, which are essential for web applications processing internationalized content.
The technical implementation of this vulnerability occurs in multiple source files within the mbstring extension's oniguruma engine including regcomp.c, regexec.c, regparse.c, unicode.c, and utf32_be.c. When PHP processes multibyte regular expression patterns containing invalid multibyte sequences, the buffer over-read conditions cause memory access violations that can lead to unpredictable behavior. The flaw stems from insufficient validation of multibyte character sequences before they are processed by the regular expression engine, allowing attackers to craft malicious input that triggers memory corruption during pattern matching operations. This type of vulnerability falls under CWE-125, which specifically addresses out-of-bounds read conditions, and represents a classic example of memory safety issues in string processing libraries.
The operational impact of CVE-2019-9023 extends beyond simple denial of service scenarios, as buffer over-read conditions can potentially enable remote code execution in certain circumstances. Attackers can exploit this vulnerability by submitting carefully crafted multibyte regular expression patterns that contain invalid sequences, which may cause the application to read beyond allocated memory boundaries. This could result in information disclosure, application crashes, or potentially allow attackers to execute arbitrary code on vulnerable systems. The vulnerability is particularly concerning for web applications that process user input through regular expression functions, as it represents a direct path for exploitation in environments where PHP handles internationalized text data. The ATT&CK framework categorizes this as a memory corruption vulnerability that can be leveraged for privilege escalation and system compromise.
Mitigation strategies for CVE-2019-9023 primarily focus on immediate patching of affected PHP installations to versions that contain the necessary security fixes. Organizations should prioritize updating their PHP environments to the patched versions including PHP 5.6.40, 7.1.26, 7.2.14, and 7.3.1, which contain the corrected buffer handling routines in the oniguruma engine. Additionally, implementing proper input validation and sanitization measures can help reduce the attack surface by filtering out malformed multibyte sequences before they reach the regular expression processing functions. Security monitoring should include detection of unusual regular expression patterns and malformed multibyte inputs that might indicate exploitation attempts. Organizations should also consider implementing web application firewalls and runtime protection mechanisms to detect and block suspicious pattern matching operations that could trigger the buffer over-read conditions. The vulnerability demonstrates the importance of maintaining up-to-date software libraries and highlights the critical nature of proper memory management in string processing functions within server-side scripting environments.