CVE-2016-5096 in PHP
Summary
by MITRE
Integer overflow in the fread function in ext/standard/file.c in PHP before 5.5.36 and 5.6.x before 5.6.22 allows remote attackers to cause a denial of service or possibly have unspecified other impact via a large integer in the second argument.
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Analysis
by VulDB Data Team • 09/13/2022
The vulnerability identified as CVE-2016-5096 represents a critical integer overflow flaw within PHP's file handling mechanisms that affects versions prior to 5.5.36 and 5.6.22. This issue resides in the ext/standard/file.c source file where the fread function processes data reading operations. The flaw manifests when a large integer value is passed as the second argument to the fread function, which then triggers an integer overflow condition during internal calculations. Such overflow conditions are particularly dangerous in programming contexts where buffer sizes or data limits are calculated using integer arithmetic, as they can lead to unpredictable behavior and system instability.
The technical implementation of this vulnerability stems from improper validation of input parameters within the fread function's internal logic. When an attacker supplies an excessively large integer value as the read size parameter, the arithmetic operations used to determine buffer allocation or data processing limits can overflow beyond the maximum representable value for the integer type. This overflow can cause the function to allocate insufficient memory, process data incorrectly, or trigger memory corruption patterns that manifest as system crashes or unexpected behavior. The vulnerability operates at the boundary conditions of integer arithmetic where signed integer overflow occurs, making it susceptible to exploitation through carefully crafted input values that exceed normal operational parameters.
From an operational perspective, this vulnerability presents significant risks to web applications running vulnerable PHP versions, as it can be exploited remotely through web interfaces that utilize file reading operations. Attackers can leverage this flaw to cause denial of service conditions by triggering system crashes or resource exhaustion, effectively making web applications unavailable to legitimate users. The unspecified other impacts mentioned in the CVE description suggest that beyond simple denial of service, the overflow could potentially enable more sophisticated exploitation techniques, including memory corruption that might allow for arbitrary code execution under certain conditions. This makes the vulnerability particularly concerning for web servers hosting multiple applications that rely on PHP's file handling capabilities.
The impact of CVE-2016-5096 aligns with CWE-190, which specifically addresses integer overflow and underflow conditions in software implementations. This classification emphasizes the fundamental nature of the flaw as an arithmetic error that occurs when operations exceed the range of the data type used to store results. The vulnerability also maps to several ATT&CK techniques including T1499 for network denial of service and potentially T1059 for command execution if exploitation leads to code execution capabilities. Organizations running affected PHP versions face immediate risk of service disruption and potential compromise of their web infrastructure, particularly those with applications that process user-provided data through file reading operations.
Mitigation strategies for CVE-2016-5096 primarily involve immediate patching of PHP installations to versions 5.5.36 or 5.6.22 and later, which contain the necessary fixes to prevent integer overflow conditions in the fread function. System administrators should also implement input validation measures that restrict the range of values accepted for file reading operations, particularly when dealing with user-supplied data. Additional protective measures include monitoring for unusual file access patterns, implementing web application firewalls to detect and block malicious input, and conducting regular security assessments of PHP-based applications to identify potential exploitation vectors. Organizations should also consider implementing application-level restrictions on file operations and ensuring that all PHP installations are kept current with security updates to prevent similar vulnerabilities from being exploited in the future.