CVE-2002-0751 in csMailto
Summary
by MITRE
CGIscript.net csMailto.cgi program allows remote attackers to use csMailto as a "spam proxy" and send mail to arbitrary users via modified (1) form-to, (2) form-from, and (3) form-results parameters.
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Analysis
by VulDB Data Team • 07/21/2019
The vulnerability identified as CVE-2002-0751 resides within the CGIscript.net csMailto.cgi program, a web-based email forwarding utility that was widely deployed in the early 2000s for enabling web forms to send emails. This particular flaw represents a classic example of improper input validation and trust model exploitation, where the application fails to properly sanitize user-supplied data before using it in email transmission contexts. The vulnerability operates through a combination of three specific parameters within the form processing mechanism that controls email routing and identification, creating a pathway for malicious actors to manipulate the email flow.
The technical exploitation of this vulnerability occurs through manipulation of three critical form parameters: form-to, form-from, and form-results. Attackers can modify these parameters to redirect email messages to arbitrary recipients, spoof sender addresses, and potentially control where email responses are delivered. This creates a scenario where the legitimate email functionality becomes a vehicle for spam distribution, as the application blindly trusts the input values provided by users without proper validation or sanitization. The flaw essentially allows attackers to use the compromised system as a spam proxy, leveraging the legitimate email infrastructure to send unsolicited messages to targets of their choosing.
The operational impact of this vulnerability extends beyond simple spam distribution, as it fundamentally undermines the trust model of the web application and creates potential for more sophisticated attacks. When an attacker successfully exploits this vulnerability, they can send spam emails that appear to originate from the compromised server, potentially leading to reputation damage for the affected organization and possible blacklisting of their email infrastructure. The vulnerability also creates opportunities for phishing attacks, where malicious actors can craft deceptive emails that appear to come from legitimate sources within the organization. This type of vulnerability is particularly dangerous in enterprise environments where email systems are often integrated with other business applications and where the compromised server might be used to send emails to large recipient lists.
Security practitioners should note that this vulnerability aligns with several common weakness enumerations including CWE-20, which describes improper input validation, and CWE-79, which covers cross-site scripting vulnerabilities that can be leveraged for similar purposes. The attack pattern follows principles outlined in the MITRE ATT&CK framework under the technique T1192, which involves the use of legitimate credentials and services to conduct malicious activities. Organizations should implement immediate mitigations including input validation and sanitization of all user-supplied parameters, implementation of strict access controls on email relay functionality, and monitoring for unusual email traffic patterns. The most effective remediation involves modifying the csMailto.cgi program to validate all form parameters against predefined acceptable values and to implement proper authentication checks before allowing email transmission. Additionally, network-level controls such as email filtering and rate limiting can provide additional protection against abuse of this vulnerability.
This vulnerability demonstrates the critical importance of proper input validation in web applications, particularly those handling user-generated content that will be used in sensitive operations such as email transmission. The flaw serves as a historical example of how simple parameter manipulation can create significant security risks, and it underscores the need for robust security testing practices including penetration testing and code review processes that can identify such trust model violations. Organizations should also consider implementing email authentication mechanisms such as SPF, DKIM, and DMARC to help protect against abuse of compromised systems and to provide additional layers of security for email infrastructure.