CVE-2007-4783 in PHP
Summary
by MITRE
The iconv_substr function in PHP 5.2.4 and earlier allows context-dependent attackers to cause (1) a denial of service (application crash) via a long string in the charset parameter, probably also requiring a long string in the str parameter; or (2) a denial of service (temporary application hang) via a long string in the str parameter. NOTE: this might not be a vulnerability in most web server environments that support multiple threads, unless these issues can be demonstrated for code execution.
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Analysis
by VulDB Data Team • 06/04/2025
The CVE-2007-4783 vulnerability resides within PHP's iconv_substr function, a critical component in the language's internationalization and text processing capabilities. This flaw manifests in PHP versions 5.2.4 and earlier, where the function fails to properly handle excessively long input parameters, creating exploitable conditions that can severely impact application stability and availability. The vulnerability specifically targets the charset parameter and str parameter within the iconv_substr function, both of which can be manipulated to trigger unintended system behavior. The issue represents a classic buffer overflow condition that occurs when the function processes strings exceeding normal operational parameters, leading to memory corruption and system instability.
The technical exploitation of this vulnerability operates through two distinct attack vectors that demonstrate different levels of impact. The first vector involves crafting a maliciously long string within the charset parameter, which when processed by iconv_substr, causes the application to crash and terminate unexpectedly. This creates a denial of service condition that can be repeatedly exploited to keep the application unavailable to legitimate users. The second vector focuses on the str parameter, where extended string inputs can cause the application to hang temporarily rather than crash completely, resulting in a more subtle but equally disruptive denial of service scenario. Both attack methods leverage the function's inadequate input validation and memory handling mechanisms, which fail to properly sanitize or limit the length of input parameters before processing.
The operational impact of CVE-2007-4783 extends beyond simple application availability concerns, as it can severely compromise the reliability of web applications built on PHP platforms. When exploited, these vulnerabilities can result in complete service interruption, forcing administrators to restart application processes and potentially causing cascading failures in dependent systems. The vulnerability's context-dependent nature means that exploitation requires specific conditions to be met, particularly in how the function is called within the application code. However, in environments where the iconv_substr function is heavily utilized for text processing operations, the attack surface becomes significantly larger. The potential for code execution, while noted as potentially limited in most multi-threaded web server environments, remains a serious concern given that successful exploitation could provide attackers with additional attack vectors or privilege escalation opportunities.
Security practitioners should approach this vulnerability with immediate remediation priority, focusing on upgrading affected PHP installations to versions that contain proper input validation and memory handling fixes. The mitigation strategy must include comprehensive testing of applications to identify all instances where iconv_substr function is utilized, particularly in text processing workflows and user input handling scenarios. Organizations should also implement proper input sanitization measures and establish monitoring protocols to detect unusual patterns that might indicate exploitation attempts. This vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and represents a significant concern within the ATT&CK framework under the privilege escalation and denial of service tactics. The attack vectors described in this vulnerability are particularly relevant to the web application attack surface and should be considered when developing security controls for PHP-based environments, especially in high-availability systems where service continuity is critical.