CVE-2003-1302 in PHP
Summary
by MITRE
The IMAP functionality in PHP before 4.3.1 allows remote attackers to cause a denial of service via an e-mail message with a (1) To or (2) From header with an address that contains a large number of "\" (backslash) characters.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 06/29/2021
The vulnerability described in CVE-2003-1302 represents a classic denial of service flaw affecting PHP's IMAP functionality prior to version 4.3.1. This weakness specifically targets the email parsing mechanisms within PHP's IMAP extension, which is commonly used for handling email messages in web applications and server-side email processing systems. The vulnerability exploits a fundamental parsing issue that occurs when PHP encounters email headers containing excessive backslash characters, creating a condition where the system becomes unresponsive or crashes during message processing. This type of vulnerability falls under the category of resource exhaustion attacks, where malicious input causes the application to consume excessive computational resources or memory, ultimately leading to system unavailability. The flaw demonstrates how seemingly benign email header data can be weaponized to disrupt service availability, making it particularly dangerous in environments where email processing is critical to application functionality.
The technical root cause of this vulnerability lies in the inadequate input validation and buffer handling within PHP's IMAP parsing routines. When PHP processes email headers containing numerous backslash characters, the parsing algorithm fails to properly handle the escaping sequences, leading to recursive or excessive memory allocation patterns. This behavior creates a condition where the system's processing time increases exponentially with the number of backslashes present in the header, effectively allowing an attacker to craft malicious email messages that can overwhelm the server resources. The vulnerability specifically affects the To and From header fields, which are fundamental components of email messages and are processed automatically during message handling. According to CWE standards, this represents a CWE-129: Improper Validation of Array Index, as the parsing logic fails to validate the length and complexity of header values before processing them. The attack pattern aligns with ATT&CK technique T1499.004: Network Denial of Service, where adversaries exploit application-level vulnerabilities to disrupt service availability.
The operational impact of CVE-2003-1302 extends beyond simple service disruption to potentially compromise entire email processing pipelines and web applications that rely on PHP's IMAP functionality. Attackers can exploit this vulnerability by simply sending an email message with a specially crafted header containing hundreds or thousands of backslash characters, causing the target server to become unresponsive and unable to process legitimate email traffic. This vulnerability is particularly dangerous in shared hosting environments or applications that process large volumes of email messages, as it can be used to systematically disrupt services without requiring sophisticated attack infrastructure. The vulnerability affects both web applications and server-side email processing systems, making it a widespread concern for organizations that depend on PHP-based email handling capabilities. Organizations running vulnerable PHP versions face significant risk of service degradation or complete system outages, especially during peak email processing periods. The impact is further amplified because the attack requires minimal effort from adversaries, making it an attractive vector for automated denial of service attacks.
Mitigation strategies for CVE-2003-1302 primarily focus on immediate patching and implementation of input validation measures. The most effective solution is upgrading to PHP version 4.3.1 or later, where the vulnerability has been addressed through improved input validation and buffer handling in the IMAP parsing routines. Organizations should also implement email header length restrictions and backslash character limits as part of their email processing security policies, preventing malicious input from reaching the vulnerable parsing functions. Network-level protections such as email filtering systems can be configured to detect and block messages containing excessive backslash characters in header fields. Additionally, implementing proper resource limits and timeouts for email processing operations can help contain the impact of successful attacks by preventing indefinite resource consumption. Security teams should also consider implementing monitoring and alerting for unusual email processing patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of validating all external input, particularly in parsing functions that handle user-supplied data, and demonstrates how seemingly simple parsing operations can become critical security concerns when not properly secured against malformed input patterns.