CVE-2014-2020 in PHP
Summary
by MITRE
ext/gd/gd.c in PHP 5.5.x before 5.5.9 does not check data types, which might allow remote attackers to obtain sensitive information by using a (1) string or (2) array data type in place of a numeric data type, as demonstrated by an imagecrop function call with a string for the x dimension value, a different vulnerability than CVE-2013-7226.
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Analysis
by VulDB Data Team • 02/01/2022
The vulnerability identified as CVE-2014-2020 affects PHP versions 5.5.x before 5.5.9 and resides within the ext/gd/gd.c file, specifically concerning the imagecrop function implementation. This flaw represents a classic type confusion vulnerability where the application fails to properly validate data types before processing them, creating a pathway for malicious input manipulation. The issue manifests when developers or attackers provide string or array data types in place of expected numeric values, particularly when invoking the imagecrop function with a string value for the x dimension parameter. This vulnerability operates under the broader category of improper input validation, which is classified as CWE-20 in the Common Weakness Enumeration catalog, and falls within the ATT&CK technique T1059.007 for input validation bypass.
The technical implementation of this vulnerability exploits PHP's loose type checking behavior, where variables can be implicitly converted between different data types without explicit type validation. When the imagecrop function processes a string value instead of a numeric value for coordinate dimensions, the underlying GD library does not properly sanitize or validate the input type before proceeding with image processing operations. This type confusion allows attackers to manipulate memory layout or access unintended data segments that might contain sensitive information, potentially leading to information disclosure. The vulnerability is particularly concerning because it leverages the legitimate GD library functionality while introducing unexpected behavior through improper type handling, making it difficult to detect through standard security scanning mechanisms.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially be exploited to gain insights into memory structures or application state that could aid in more sophisticated attacks. Attackers can craft malicious inputs that, when processed through the imagecrop function, may cause the application to leak memory contents or sensitive data from adjacent memory locations. This type of vulnerability is particularly dangerous in web applications where image processing is common, as it can be triggered through user-uploaded images or manipulated parameters in image manipulation endpoints. The vulnerability demonstrates how seemingly benign functions can become attack vectors when proper input validation is omitted, representing a fundamental security flaw in the application's defensive posture.
Mitigation strategies for CVE-2014-2020 primarily involve upgrading to PHP 5.5.9 or later versions where the type checking has been properly implemented within the GD library. Organizations should also implement strict input validation at application level, ensuring that all numeric parameters are explicitly validated and converted to appropriate data types before being passed to image processing functions. Additionally, implementing proper error handling and input sanitization routines can help detect and prevent malformed inputs from reaching vulnerable functions. Security teams should consider implementing application firewalls or web application security controls that can monitor for unusual parameter patterns and flag potential exploitation attempts. The vulnerability serves as a reminder of the importance of defensive programming practices and proper type validation, particularly in libraries that handle user-supplied data in critical system functions.