CVE-2017-9120 in PHP
Summary
by MITRE
PHP 7.x through 7.1.5 allows remote attackers to cause a denial of service (buffer overflow and application crash) or possibly have unspecified other impact via a long string because of an Integer overflow in mysqli_real_escape_string.
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Analysis
by VulDB Data Team • 04/29/2023
The vulnerability identified as CVE-2017-9120 represents a critical buffer overflow condition affecting PHP versions 7.0 through 7.1.5, specifically within the mysqli_real_escape_string function. This flaw stems from an integer overflow issue that occurs when processing exceptionally long strings, creating a scenario where malicious input can trigger system instability. The vulnerability falls under the category of CWE-190, Integer Overflow or Wraparound, which is classified as a fundamental weakness in software design that can lead to severe security implications. The affected function mysqli_real_escape_string is commonly used in database interaction code to escape special characters in strings before SQL queries are executed, making this vulnerability particularly dangerous in web applications that handle user input.
The technical exploitation of this vulnerability occurs when an attacker submits a specially crafted string that exceeds the maximum integer value that can be handled by the underlying data structures within PHP's mysqli extension. When the mysqli_real_escape_string function processes this oversized string, the integer overflow causes the buffer allocation to wrap around to a small value, resulting in insufficient memory allocation for the operation. This misallocation leads to memory corruption that can manifest as buffer overflows, application crashes, or potentially more severe consequences including arbitrary code execution. The vulnerability is particularly concerning because it operates at the core database interaction layer, where it can be triggered through various input vectors including form submissions, API endpoints, or file uploads that pass user data through database queries.
The operational impact of CVE-2017-9120 extends beyond simple denial of service conditions to potentially enable more sophisticated attacks depending on the system configuration and memory layout. When the buffer overflow occurs, applications may crash unpredictably, leading to service disruption for legitimate users and creating opportunities for attackers to perform reconnaissance activities or establish persistent access patterns. The vulnerability can be leveraged through the ATT&CK technique of Resource Exhaustion or by exploiting the Memory Corruption tactic, where attackers manipulate memory structures to achieve unauthorized system access. In environments where PHP applications handle sensitive data through database connections, this vulnerability creates a potential pathway for data exfiltration or system compromise, as the application crash may expose debugging information or create opportunities for further exploitation.
Mitigation strategies for CVE-2017-9120 primarily focus on immediate version upgrades to PHP 7.1.6 or later, which contain the necessary patches to address the integer overflow condition in mysqli_real_escape_string. System administrators should also implement input validation controls that limit the length of strings processed through database functions, effectively creating a defense-in-depth approach that reduces the likelihood of exploitation even if the underlying vulnerability remains unpatched. Additional protective measures include monitoring application logs for unusual patterns of memory allocation failures or application crashes that may indicate exploitation attempts, implementing web application firewalls to filter suspicious input patterns, and conducting regular security assessments to identify other potential vulnerabilities in the PHP application stack. Organizations should also consider applying runtime protections such as stack canaries or address space layout randomization to make exploitation more difficult and detectable. The vulnerability demonstrates the importance of maintaining up-to-date software versions and implementing comprehensive security monitoring procedures to detect and respond to exploitation attempts effectively.