CVE-2007-3998 in PHP
Summary
by MITRE
The wordwrap function in PHP 4 before 4.4.8, and PHP 5 before 5.2.4, does not properly use the breakcharlen variable, which allows remote attackers to cause a denial of service (divide-by-zero error and application crash, or infinite loop) via certain arguments, as demonstrated by a chr(0), 0, "" argument set.
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Analysis
by VulDB Data Team • 07/25/2019
The vulnerability described in CVE-2007-3998 represents a critical flaw in PHP's wordwrap function implementation that affects versions prior to PHP 4.4.8 and PHP 5.2.4. This issue resides in the core string manipulation functionality of the PHP runtime environment, making it particularly dangerous as it can be exploited through standard web application interactions. The vulnerability specifically targets the breakcharlen variable handling within the wordwrap function, which is commonly used in web applications for formatting text output and managing line breaks in content rendering.
The technical exploitation of this vulnerability occurs when malicious input is passed to the wordwrap function with specific argument combinations including chr(0), 0, and empty string values. The flaw manifests as improper handling of the breakcharlen variable which leads to arithmetic exceptions and application instability. When the function processes these particular inputs, it can trigger a divide-by-zero error that causes the PHP interpreter to crash or enter an infinite loop state, effectively rendering the web application unavailable to legitimate users. This type of vulnerability falls under the CWE-369 weakness category, specifically related to the use of a division operation without proper validation of the divisor, and can be classified as a denial of service condition within the ATT&CK framework under the privilege escalation and denial of service tactics.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged by remote attackers to cause widespread availability issues across web applications. Since PHP is one of the most widely used server-side scripting languages, the potential attack surface is enormous, affecting countless websites and web applications that rely on proper text formatting capabilities. The vulnerability is particularly concerning because it requires no special privileges to exploit and can be triggered through standard HTTP requests, making it an attractive target for automated attacks. Additionally, the infinite loop condition can consume significant system resources, potentially leading to server exhaustion and cascading failures that affect multiple applications running on the same infrastructure.
Mitigation strategies for this vulnerability involve immediate patching of affected PHP installations to versions 4.4.8 and 5.2.4 or later where the issue has been resolved through proper validation of the breakcharlen variable. System administrators should also implement input validation measures at the application level to sanitize any user-provided data that might be passed to wordwrap functions, particularly when dealing with text processing operations. Network-level protections such as web application firewalls can provide additional defense-in-depth by monitoring for suspicious argument patterns that match the known exploit vectors. Organizations should also conduct thorough vulnerability assessments to identify all instances of vulnerable PHP versions across their infrastructure and prioritize remediation efforts based on risk assessment. The fix implemented in the patched versions demonstrates proper error handling through validation of the break character length parameter, preventing the arithmetic operations that lead to system instability while maintaining the intended functionality of the wordwrap function.