CVE-2016-4073 in Mac OS X
Summary
by MITRE
Multiple integer overflows in the mbfl_strcut function in ext/mbstring/libmbfl/mbfl/mbfilter.c in PHP before 5.5.34, 5.6.x before 5.6.20, and 7.x before 7.0.5 allow remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted mb_strcut call.
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Analysis
by VulDB Data Team • 08/19/2022
The vulnerability identified as CVE-2016-4073 represents a critical security flaw within PHP's multibyte string handling functionality, specifically affecting the mbfl_strcut function implementation. This issue resides in the ext/mbstring/libmbfl/mbfl/mbfilter.c file and impacts multiple PHP version streams including 5.5.x before 5.5.34, 5.6.x before 5.6.20, and 7.x before 7.0.5. The flaw manifests as multiple integer overflows that occur during the processing of multibyte character strings, creating a pathway for malicious actors to exploit the application's memory management mechanisms. The vulnerability is particularly concerning because it can be triggered through crafted input passed to the mb_strcut function, which is commonly used in web applications for string manipulation tasks involving international character sets.
The technical nature of this vulnerability stems from improper handling of integer arithmetic within the mbfl_strcut function, where developers failed to implement adequate bounds checking for integer operations. When the function processes multibyte character data, it performs calculations that can exceed the maximum representable value for integer data types, leading to integer overflow conditions. These overflow scenarios can result in unpredictable behavior where the application's memory layout becomes corrupted, potentially allowing attackers to manipulate memory pointers or overwrite critical application data structures. The vulnerability's classification aligns with CWE-190, which specifically addresses integer overflow and underflow conditions, and the attack surface extends to the ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion or application crashes.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as the integer overflow conditions can potentially be leveraged to execute arbitrary code on affected systems. Remote attackers can craft malicious input strings that, when processed by the mb_strcut function, trigger the overflow conditions and cause the application to crash or potentially provide an execution environment for malicious code. This makes the vulnerability particularly dangerous in web server environments where PHP applications process user input from untrusted sources. The risk is amplified because the vulnerable function is commonly used in web applications for handling international text processing, making it a frequent target for exploitation. Attackers can exploit this vulnerability without requiring special privileges or authentication, as the flaw exists in the core string manipulation functionality that many applications depend upon.
Mitigation strategies for CVE-2016-4073 should prioritize immediate patching of affected PHP installations to the latest secure versions, specifically PHP 5.5.34, 5.6.20, or 7.0.5 and later. Organizations should implement input validation measures that sanitize all multibyte character data before processing through string manipulation functions, particularly when dealing with user-supplied input. Additionally, application-level protections such as implementing proper error handling and memory management practices can help reduce the impact of potential exploitation attempts. Network-level defenses including web application firewalls and intrusion detection systems should be configured to monitor for suspicious patterns in multibyte string processing that could indicate exploitation attempts. Security teams should also conduct comprehensive vulnerability assessments to identify all instances where mb_strcut or related functions are used within their applications and ensure that proper bounds checking and input sanitization measures are implemented throughout the codebase. The vulnerability demonstrates the critical importance of proper integer arithmetic handling in security-critical applications and serves as a reminder of the need for comprehensive code review processes that examine mathematical operations for potential overflow conditions.