CVE-2007-4887 in PHP
Summary
by MITRE
The dl function in PHP 5.2.4 and earlier allows context-dependent attackers to cause a denial of service (application crash) via a long string in the library parameter. NOTE: there are limited usage scenarios under which this would be a vulnerability.
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Analysis
by VulDB Data Team • 07/27/2019
The vulnerability described in CVE-2007-4887 represents a denial of service flaw within the dynamic loading functionality of PHP versions 5.2.4 and earlier. This issue specifically targets the dl function which is responsible for loading dynamic extensions into the PHP runtime environment. The vulnerability manifests when an attacker provides an excessively long string as the library parameter to the dl function, causing the application to crash and resulting in a denial of service condition that affects the availability of the web application.
The technical root cause of this vulnerability lies in the insufficient input validation and boundary checking within the dl function implementation. When PHP processes the library parameter, it fails to properly handle or limit the length of strings passed to this function, creating a potential buffer overflow condition or memory corruption scenario. This flaw operates under context-dependent conditions, meaning that the vulnerability only presents itself when specific environmental factors align, such as when the dl function is actually invoked with malicious input. The limited usage scenarios mentioned in the original description indicate that this vulnerability requires particular conditions to be exploitable, potentially limiting its widespread impact but not eliminating the risk entirely.
From an operational impact perspective, this vulnerability can severely disrupt web application availability and service continuity. When exploited, the denial of service condition causes the PHP application to crash, requiring system administrators to restart the web server or application services to restore functionality. This type of vulnerability is particularly concerning in production environments where application uptime is critical, as it can be leveraged by attackers to perform service disruption attacks. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of how insufficient input validation can lead to application instability and service disruption.
The mitigation strategies for CVE-2007-4887 primarily involve upgrading to PHP versions that have addressed this vulnerability, specifically PHP 5.2.5 and later releases. System administrators should also implement proper input validation and sanitization measures to prevent malformed strings from reaching the dl function. Additionally, the principle of least privilege should be applied by restricting the use of the dl function to only those environments where dynamic extension loading is absolutely necessary. Organizations should also consider implementing network-level controls and monitoring to detect unusual patterns of dl function usage that might indicate attempted exploitation. This vulnerability demonstrates the importance of maintaining current software versions and the critical nature of input validation in preventing both denial of service and potential privilege escalation scenarios that could arise from similar buffer overflow conditions. The ATT&CK framework categorizes this under privilege escalation and denial of service techniques, highlighting the potential for broader exploitation beyond simple service disruption.