CVE-2005-1807 in PHPMailer
Summary
by MITRE
The Data function in class.smtp.php in PHPMailer 1.7.2 and earlier allows remote attackers to cause a denial of service (infinite loop leading to memory and CPU consumption) via a long header field.
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Analysis
by VulDB Data Team • 02/24/2025
The vulnerability described in CVE-2005-1807 represents a critical denial of service weakness within the PHPMailer library version 1.7.2 and earlier. This flaw exists in the Data function of the class.smtp.php file, which is a core component of the email sending functionality in PHP applications. The vulnerability specifically targets the handling of email header fields, creating a condition where malformed or excessively long header data can trigger an infinite loop during processing. This issue demonstrates a classic example of inadequate input validation and error handling within email processing libraries that are widely used across web applications.
The technical implementation of this vulnerability stems from how PHPMailer processes email headers when constructing the message data. When a remote attacker supplies a header field that exceeds normal length parameters, the Data function fails to properly validate or limit the header length, resulting in a condition where the processing loop continues indefinitely. The flaw operates by exploiting the lack of boundary checks on header field lengths, causing the application to enter an infinite loop that consumes both memory and cpu resources at an exponential rate. This type of vulnerability falls under CWE-674, which specifically addresses uncontrolled resource consumption, and represents a form of resource exhaustion attack that can be executed without authentication.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire web applications that rely on PHPMailer for email functionality. Attackers can exploit this weakness by crafting specially formatted email headers that trigger the infinite loop, causing the target server to consume all available memory and cpu cycles, effectively rendering the application unavailable to legitimate users. This vulnerability is particularly dangerous in shared hosting environments or applications with limited resource allocation, where a single malicious email could cause cascading failures across multiple services. The attack vector requires no authentication and can be executed through any means that allows email header injection, making it highly accessible to potential attackers.
Mitigation strategies for CVE-2005-1807 should focus on immediate version upgrades to PHPMailer 1.7.3 or later, which contain the necessary patches to prevent header length validation issues. Organizations should also implement input sanitization measures that validate and truncate header fields to reasonable lengths before processing, and consider implementing resource limits and monitoring to detect unusual memory and cpu consumption patterns. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a critical weakness that should be addressed through comprehensive security auditing of all email processing components within web applications. Additionally, implementing proper error handling and timeout mechanisms in email processing functions can help prevent exploitation of similar resource exhaustion vulnerabilities in other components of the application stack.