CVE-2002-0986 in PHP
Summary
by MITRE
The mail function in PHP 4.x to 4.2.2 does not filter ASCII control characters from its arguments, which could allow remote attackers to modify mail message content, including mail headers, and possibly use PHP as a "spam proxy."
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Analysis
by VulDB Data Team • 09/10/2025
The vulnerability described in CVE-2002-0986 represents a critical security flaw in PHP versions 4.x through 4.2.2 that specifically affects the mail function implementation. This issue stems from inadequate input validation and sanitization of mail function arguments, creating a pathway for malicious actors to exploit the system's email handling capabilities. The flaw exists at the core of PHP's mail functionality where ASCII control characters are not properly filtered, allowing attackers to inject malicious content into email headers and message bodies.
The technical exploitation of this vulnerability occurs when PHP's mail function processes user-supplied input without adequate sanitization of control characters such as carriage return, line feed, and other ASCII codes below 32. When these unfiltered characters are passed to the mail function, they can be interpreted by mail servers and clients as command sequences rather than simple text data. Attackers can leverage this weakness to manipulate email headers including From, To, Subject, and other header fields, potentially redirecting messages or injecting malicious content. The vulnerability creates a scenario where PHP systems can be coerced into acting as spam relays or proxies, as attackers can craft email messages that bypass normal email filtering mechanisms through header injection techniques.
The operational impact of CVE-2002-0986 extends beyond simple message manipulation to encompass potential abuse as a spam proxy mechanism. Systems running vulnerable PHP versions become susceptible to being used for unauthorized email sending, potentially leading to spam distribution and reputation damage for the affected organizations. The vulnerability also poses risks to email server security as injected headers could be used to exploit other weaknesses in email infrastructure. This issue particularly affects web applications that rely on PHP's mail function for user communication, automated notifications, or contact form submissions where user input is directly passed to the mail function without proper validation.
This vulnerability aligns with CWE-174, which addresses the weakness of insufficient control of information flow, and can be mapped to ATT&CK technique T1190, which covers the exploitation of vulnerabilities in email servers. Organizations should implement immediate mitigations including upgrading to PHP versions 4.2.3 or later where this vulnerability has been addressed, implementing strict input validation for all mail function arguments, and filtering ASCII control characters from user-supplied data. Additional protective measures include configuring email servers to reject messages with malformed headers, implementing rate limiting for email sending functions, and conducting regular security audits of web applications that utilize PHP's mail functionality to ensure proper input sanitization practices are in place.