CVE-1999-1535 is a critical buffer overflow vulnerability found in the AspUpload.dll component of Persits Software's AspUpload product versions prior to 1.4.0.2. AspUpload is a widely used Active Server Pages (ASP) component that facilitates file uploads in web applications. The vulnerability arises when the component processes HTTP requests containing excessively long arguments. Specifically, a remote attacker can craft an HTTP request with an overly long parameter that overflows the buffer allocated in AspUpload.dll. This overflow can corrupt memory, leading to a denial of service (DoS) by crashing the web application or web server. More critically, the vulnerability may allow an attacker to execute arbitrary code remotely, potentially gaining control over the affected server. The CVSS v2 score of 10.0 reflects the highest severity, indicating that the vulnerability is remotely exploitable over the network without authentication, requires no user interaction, and impacts confidentiality, integrity, and availability. Although this vulnerability was published in 1999 and no official patch is available, it remains a significant risk for legacy systems still running vulnerable versions of AspUpload. Exploitation would typically target web servers hosting ASP applications that rely on the vulnerable AspUpload.dll for file upload functionality. The lack of known exploits in the wild may be due to the age of the vulnerability and the declining use of this component, but the potential impact remains severe if exploited.

For European organizations, the impact of CVE-1999-1535 can be substantial, especially for those operating legacy web applications using vulnerable versions of AspUpload. Successful exploitation can lead to complete compromise of web servers, resulting in unauthorized access to sensitive data, defacement of websites, disruption of business operations through denial of service, and potential lateral movement within internal networks. Given the critical nature of the vulnerability, attackers could leverage it to implant malware, steal confidential information, or disrupt services critical to business continuity. Organizations in sectors such as finance, healthcare, government, and critical infrastructure, which often maintain legacy systems, are particularly at risk. Additionally, the vulnerability's ability to compromise confidentiality, integrity, and availability simultaneously elevates the threat level. The absence of a patch means that affected organizations must rely on alternative mitigation strategies to protect their environments. Failure to address this vulnerability could lead to regulatory non-compliance, reputational damage, and financial losses.

Since no official patch is available for this vulnerability, European organizations should implement the following specific mitigation measures: 1) Identify and inventory all web applications using AspUpload.dll, focusing on versions prior to 1.4.0.2. 2) Where possible, upgrade to the latest version of AspUpload that addresses this vulnerability or replace the component with a secure alternative. 3) Employ web application firewalls (WAFs) configured to detect and block HTTP requests containing abnormally long parameters or suspicious payloads targeting file upload endpoints. 4) Implement strict input validation and length checks on all user-supplied data at the application level to prevent buffer overflow attempts. 5) Isolate legacy web servers in segmented network zones with limited access to critical internal resources to contain potential compromises. 6) Monitor web server logs and network traffic for signs of exploitation attempts, such as unusual HTTP request patterns or crashes. 7) Conduct regular security assessments and penetration testing focused on legacy components. 8) Develop an incident response plan tailored to web server compromises involving legacy software. These targeted measures go beyond generic advice by focusing on detection, containment, and compensating controls in the absence of a patch.