CVE-2015-8617 in PHP
Summary
by MITRE
Format string vulnerability in the zend_throw_or_error function in Zend/zend_execute_API.c in PHP 7.x before 7.0.1 allows remote attackers to execute arbitrary code via format string specifiers in a string that is misused as a class name, leading to incorrect error handling.
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Analysis
by VulDB Data Team • 12/21/2024
The vulnerability identified as CVE-2015-8617 represents a critical format string vulnerability within PHP's Zend Engine execution API. This flaw exists in the zend_throw_or_error function located in Zend/zend_execute_API.c and affects PHP 7.x versions prior to 7.0.1. The vulnerability stems from improper handling of string formatting operations where user-supplied input is incorrectly treated as a format string rather than a literal class name. This misclassification creates a dangerous condition where attackers can inject format specifiers into error messages that are subsequently processed without proper sanitization. The vulnerability operates at the core execution layer of PHP, making it particularly dangerous as it can be exploited during normal script execution flows when class names are processed or when error conditions are triggered.
The technical exploitation of this vulnerability relies on the fundamental principle of format string attacks where attackers manipulate input to control how format specifiers are interpreted by the underlying printf family functions. In this case, when PHP processes a malformed class name that contains format specifiers such as %s, %d, or other printf directives, the zend_throw_or_error function fails to properly escape or validate this input before incorporating it into error messages. This creates a scenario where attacker-controlled data can be interpreted as format string directives, potentially leading to information disclosure, stack corruption, or arbitrary code execution. The vulnerability specifically manifests when the error handling mechanism attempts to report class-related errors, making it particularly relevant in applications that dynamically load or reference classes from user input. This flaw directly maps to CWE-134 which defines format string vulnerabilities as weaknesses that occur when a program uses a format string provided by an attacker without proper validation or sanitization.
The operational impact of CVE-2015-8617 extends beyond simple code execution to encompass potential system compromise and data breaches. Attackers can leverage this vulnerability to execute arbitrary commands on affected systems, potentially gaining full control over web servers running vulnerable PHP versions. The vulnerability is particularly concerning in web applications where user input is processed through class loading mechanisms, as it allows for remote code execution without requiring authentication. The attack surface includes any application that accepts dynamic class names or allows user input to influence class resolution processes, making it a widespread concern across PHP-based web applications. This vulnerability aligns with ATT&CK technique T1059.007 which covers the use of scripting languages for execution, and T1190 which addresses the exploitation of vulnerabilities in web applications. The severity is amplified by the fact that PHP 7.x was widely deployed, making the potential attack impact substantial across numerous organizations and applications.
Mitigation strategies for CVE-2015-8617 require immediate patching of affected PHP installations to version 7.0.1 or later where the vulnerability has been resolved through proper input validation and sanitization of class names in error handling routines. Organizations should implement comprehensive input validation at all points where class names or similar identifiers are processed, ensuring that all user-supplied data undergoes proper sanitization before being used in error reporting contexts. Network segmentation and application firewalls can provide additional defense-in-depth measures to limit the potential impact of exploitation attempts. Regular security assessments and code reviews should specifically target error handling routines and format string usage patterns to identify similar vulnerabilities. The remediation process must include thorough testing to ensure that patching does not introduce regressions in application functionality, particularly in error reporting and debugging features that depend on proper format string handling. Security monitoring should be enhanced to detect unusual patterns in error log entries that might indicate exploitation attempts. This vulnerability serves as a reminder of the critical importance of secure coding practices in core execution engines and the necessity of rigorous input validation even in fundamental system components.