CVE-1999-0173 describes a vulnerability in the FormMail CGI program developed by Matt Wright. FormMail is a widely used CGI script designed to process web form submissions and send the contents via email. The vulnerability arises because the FormMail script can be invoked and used by web servers other than the one on which it is hosted. This means that an attacker controlling a remote web server can abuse the FormMail script on a victim server to send arbitrary emails, effectively turning the vulnerable server into an open mail relay. The vulnerability does not require authentication and can be exploited remotely over the network (AV:N), with low attack complexity (AC:L). While it does not directly compromise confidentiality or availability, it impacts integrity by allowing unauthorized use of the mail sending functionality (I:P). The vulnerability was published in 1997 and has a CVSS score of 5.0 (medium severity). No patches are available, and no known exploits are currently in the wild. The core issue is the lack of proper host verification or access controls within the FormMail script, allowing it to be triggered by external servers, which can facilitate spam campaigns or phishing attacks by abusing the victim server's mail infrastructure.

For European organizations, this vulnerability can lead to their web servers being exploited as open mail relays, which can have several negative consequences. First, it can damage the organization's reputation if their mail servers are used to send spam or phishing emails, potentially leading to blacklisting by email providers and loss of trust among customers and partners. Second, it can increase the risk of targeted phishing attacks leveraging the organization's domain, increasing the likelihood of successful social engineering attacks. Third, the misuse of resources can lead to increased bandwidth and processing costs. Although the vulnerability does not directly compromise sensitive data or system availability, the indirect effects on email integrity and organizational reputation can be significant, especially for organizations relying heavily on email communications. European organizations with public-facing web servers running legacy or unpatched FormMail scripts are particularly at risk.

Given that no official patches are available for this vulnerability, European organizations should take specific steps to mitigate the risk. First, immediately audit all web servers to identify any instances of the FormMail CGI script. If found, remove or disable the script unless absolutely necessary. If the script must be used, implement strict access controls such as IP whitelisting to restrict which servers can invoke the script. Additionally, modify the FormMail script to include host verification logic to ensure it only processes requests originating from the local server. Employ web application firewalls (WAFs) to detect and block suspicious requests targeting the FormMail endpoint. Monitor outgoing email traffic for unusual patterns indicative of abuse. Finally, consider migrating to modern, actively maintained web form processing solutions that do not have this vulnerability and provide better security controls.