CVE-2023-37535 is a high-severity Cross-Site Scripting (XSS) vulnerability identified in HCL Software's HCL Domino Leap product, specifically affecting versions 1.0 through 1.0.5 and 1.1 through 1.1.2. The root cause of this vulnerability is an insufficient URI protocol whitelist implemented in both HCL Domino Volt and Domino Leap. This flaw allows an attacker to inject malicious scripts through query parameters in web requests. When a user accesses a crafted URL containing malicious payloads in the query string, the application fails to properly neutralize or sanitize these inputs during web page generation, leading to script execution in the context of the victim's browser. The CVSS 3.1 base score of 7.1 reflects the vulnerability's network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), but requires user interaction (UI:R). The impact is limited confidentiality loss (C:L), high integrity impact (I:H), and no availability impact (A:N). This means an attacker can potentially manipulate or alter data or application behavior but cannot disrupt service availability. No known exploits are currently reported in the wild, but the vulnerability's nature and ease of exploitation make it a significant risk. The vulnerability falls under CWE-79, which is a common and well-understood class of web application security issues related to improper input validation and output encoding. Since HCL Domino Leap is a platform used for rapid application development and workflow automation, exploitation could lead to unauthorized script execution, session hijacking, or data manipulation within affected applications, potentially compromising user trust and data integrity.

For European organizations using HCL Domino Leap, this vulnerability poses a significant risk to the confidentiality and integrity of their web applications and data. Given that the vulnerability allows script injection via query parameters, attackers could execute arbitrary JavaScript in the context of authenticated users, leading to session hijacking, credential theft, or unauthorized actions performed on behalf of users. This is particularly concerning for organizations handling sensitive or regulated data, such as financial institutions, healthcare providers, and government agencies. The integrity impact is high, meaning attackers could alter data or application behavior, potentially undermining business processes or compliance requirements. Although availability is not directly affected, the reputational damage and potential regulatory penalties resulting from data breaches or unauthorized access could be severe. Additionally, the requirement for user interaction (clicking a malicious link) means phishing campaigns could be an effective attack vector, increasing the threat surface. The lack of known exploits in the wild suggests that proactive patching and mitigation can prevent exploitation before widespread attacks occur.

1. Immediate patching: Although no official patch links are provided in the data, organizations should monitor HCL Software's advisories closely and apply any available updates or patches for Domino Leap versions 1.0 to 1.1.2 as soon as they are released. 2. Input validation and output encoding: Implement strict input validation on all query parameters and ensure proper output encoding on all user-supplied data rendered in web pages to prevent script injection. 3. URI protocol whitelist enhancement: Review and strengthen the URI protocol whitelist to restrict allowed protocols rigorously, preventing injection of malicious scripts via unconventional or crafted URIs. 4. Web Application Firewall (WAF): Deploy and configure WAF rules to detect and block common XSS payloads targeting query parameters in Domino Leap applications. 5. User awareness training: Educate users about the risks of clicking on suspicious links, especially those received via email or messaging platforms, to reduce the likelihood of successful phishing attacks exploiting this vulnerability. 6. Monitoring and logging: Enable detailed logging of web requests and monitor for unusual query parameter patterns or spikes in suspicious activity that could indicate exploitation attempts. 7. Application design review: For organizations developing custom applications on Domino Leap, conduct security code reviews focusing on input handling and output encoding to identify and remediate similar vulnerabilities proactively.