CVE-2002-2109 in FormMail
Summary
by MITRE
Matt Wright FormMail 1.9 and earlier allows remote attackers to bypass the HTTP_REFERER check and conduct unauthorized activities via (1) a blank referer, (2) a spoofed referer with a trusted domain/URL after the beginning of the referer, or (3) a spoofed referer with a trusted domain/URL in the beginning (hostname) portion of the referer.
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Analysis
by VulDB Data Team • 08/30/2025
The vulnerability identified as CVE-2002-2109 affects Matt Wright FormMail version 1.9 and earlier, representing a critical security flaw in web form processing applications. This vulnerability resides in the HTTP_REFERER validation mechanism that was implemented to prevent unauthorized access to form mail functionality. The flaw specifically targets the referer checking logic that was designed to ensure that form submissions originate from trusted sources within the same domain or specified domains. The implementation of this check was intended to prevent cross-site request forgery and unauthorized form submissions, but the developers failed to account for several bypass techniques that could circumvent the validation entirely.
The technical implementation of this vulnerability stems from overly simplistic referer validation logic that does not properly sanitize or thoroughly validate the referer header values. When attackers craft malicious referer headers, they can exploit three distinct bypass methods that demonstrate a fundamental flaw in the validation approach. The first bypass involves sending a blank referer header, which the application fails to properly handle and instead treats as a valid request. The second bypass technique involves crafting a referer header where a trusted domain appears somewhere within the URL path rather than at the beginning, exploiting the fact that the validation logic may perform substring matching rather than comprehensive URL parsing. The third bypass method involves placing a trusted domain at the beginning of the referer header, but with additional malicious content in the path portion, effectively tricking the validation into considering the request legitimate.
This vulnerability operates under the broader category of weak input validation and authentication bypass issues, which fall under CWE-284 Access Control Issues and CWE-346 Origin Validation. The attack vector demonstrates how simple validation mechanisms can be circumvented through careful header manipulation, representing a classic example of insufficient validation or sanitization of user-provided data. The operational impact of this vulnerability is severe as it allows remote attackers to execute unauthorized form submissions, potentially leading to spam flooding, data exfiltration, or other malicious activities. The vulnerability also demonstrates weaknesses in the principle of least privilege, where the application does not properly enforce access controls on form processing functionality.
The exploitation of this vulnerability aligns with several tactics described in the MITRE ATT&CK framework, particularly those related to initial access and privilege escalation through web application vulnerabilities. Attackers can leverage this flaw to gain unauthorized access to form mail functionality and potentially use it as a stepping stone for further attacks on the web server or network. The vulnerability also represents a significant concern for organizations using legacy web applications, as it demonstrates how basic security controls can be bypassed through relatively simple header manipulation techniques. The impact extends beyond immediate unauthorized access to include potential reputational damage from spam flooding and the possibility of using the compromised form as a vector for more sophisticated attacks.
Organizations should implement comprehensive mitigations including updating to patched versions of Matt Wright FormMail, implementing more robust referer validation that properly parses full URLs rather than relying on simple substring matching, and employing additional authentication mechanisms for critical form processing functions. The recommended approach involves implementing proper referer validation that checks the complete URL structure and validates against a whitelist of trusted domains with proper URL parsing. Additionally, organizations should consider implementing additional security controls such as CAPTCHA mechanisms, rate limiting, and more robust authentication for form processing functions to prevent unauthorized access even if referer validation is bypassed. The vulnerability serves as a reminder of the importance of thorough security testing and validation of access control mechanisms, particularly in legacy applications that may not have been designed with modern security requirements in mind.