CVE-2005-3883 in PHP
Summary
by MITRE
CRLF injection vulnerability in the mb_send_mail function in PHP before 5.1.0 might allow remote attackers to inject arbitrary e-mail headers via line feeds (LF) in the "To" address argument.
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Analysis
by VulDB Data Team • 06/12/2019
The CVE-2005-3883 vulnerability represents a critical cross-site scripting and email header injection flaw within the PHP mail function implementation. This vulnerability specifically affects the mb_send_mail function in PHP versions prior to 5.1.0, creating a pathway for malicious actors to manipulate email headers through carefully crafted input sequences. The vulnerability stems from insufficient input validation and sanitization mechanisms within the mail sending functionality, allowing attackers to inject malicious content into email headers that are subsequently processed by mail servers.
The technical flaw manifests through the improper handling of line feed characters within the "To" address parameter of the mb_send_mail function. When PHP processes email addresses containing line feed characters, these control sequences are not adequately escaped or filtered, enabling attackers to inject additional email headers such as CC, BCC, Subject, or even arbitrary commands. This CRLF (Carriage Return Line Feed) injection technique operates by leveraging the fundamental structure of email protocols where headers are separated by line terminators, creating a vector for header manipulation that bypasses normal validation checks.
The operational impact of this vulnerability extends beyond simple email header manipulation to potentially enable sophisticated attack scenarios including email spoofing, spam distribution, and server-side header injection attacks. Attackers can exploit this weakness to redirect email traffic, inject malicious content into email messages, or even execute command injection against vulnerable mail servers that process these manipulated headers. The vulnerability particularly affects web applications that utilize PHP for email functionality without proper input sanitization, making it a significant concern for applications handling user-supplied email addresses or contact information.
From a cybersecurity perspective, this vulnerability aligns with CWE-113, which specifically addresses improper neutralization of CRLF characters in HTTP headers, and maps to ATT&CK technique T1190 for exploitation of vulnerabilities in web applications. The attack surface is particularly wide as any PHP application using mb_send_mail or similar mail functions without proper input validation becomes a potential target. Organizations running PHP applications with vulnerable versions face risks of email-based attacks that could compromise email server configurations or be used as stepping stones for broader network infiltration attempts.
Mitigation strategies for CVE-2005-3883 require immediate application of PHP version updates to 5.1.0 or later, where the vulnerability has been addressed through improved input validation mechanisms. Additionally, developers should implement comprehensive input sanitization for all email address parameters, including explicit filtering of control characters and line terminators. Security measures should incorporate proper header validation, use of parameterized email sending functions, and regular security audits of email handling code. Organizations should also consider implementing email gateway filtering and monitoring systems to detect anomalous header injection patterns that might indicate exploitation attempts. The vulnerability underscores the critical importance of keeping PHP installations updated and maintaining robust input validation practices in web applications that handle user-generated email data.