CVE-2021-21087 is a Cross-site Scripting (XSS) vulnerability identified in Adobe ColdFusion versions 2016 (update 16 and earlier), 2018 (update 10 and earlier), and 2021.0.0.323925. This vulnerability arises due to improper neutralization of user input during web page generation, classified under CWE-79. An attacker exploiting this flaw can inject and execute arbitrary JavaScript code within the context of the affected user's browser session. The attack vector requires user interaction, meaning the victim must click a malicious link or visit a crafted web page to trigger the exploit. The vulnerability does not appear to have publicly known exploits in the wild as of the published date. Adobe ColdFusion is a commercial rapid web application development platform widely used for building enterprise web applications, APIs, and services. The vulnerability could allow attackers to perform actions such as session hijacking, credential theft, or redirecting users to malicious sites, compromising confidentiality and integrity of user data. Since the flaw is client-side and requires user interaction, the attack surface is limited to users who access vulnerable ColdFusion-powered web applications. No official patches or updates are linked in the provided information, but Adobe typically releases security updates to address such issues. The vulnerability was reserved in December 2020 and published in April 2021, indicating it has been known for some time but without widespread exploitation reported.

For European organizations, the impact of CVE-2021-21087 depends largely on their use of Adobe ColdFusion in public-facing or internal web applications. Exploitation could lead to unauthorized execution of scripts in users' browsers, potentially resulting in theft of session cookies, user credentials, or sensitive data. This could facilitate further attacks such as account takeover or lateral movement within the organization. Given the medium severity and requirement for user interaction, the risk is moderate but non-negligible, especially for organizations with high-value data or critical services exposed via ColdFusion applications. Sectors such as finance, government, healthcare, and critical infrastructure in Europe could face reputational damage, regulatory penalties (e.g., GDPR violations due to data breaches), and operational disruptions if exploited. The vulnerability could also be leveraged in targeted phishing campaigns to trick users into triggering the XSS payload. However, the lack of known active exploitation reduces immediate risk, though the presence of unpatched systems could invite opportunistic attackers.

1. Immediate application of the latest Adobe ColdFusion security updates and patches is essential once available. 2. Implement strict input validation and output encoding on all user-supplied data within ColdFusion applications to prevent injection of malicious scripts. 3. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. 4. Conduct security audits and code reviews focusing on areas where user input is reflected in web pages. 5. Educate users and administrators about the risks of clicking unknown links or visiting untrusted sites to reduce the likelihood of user interaction-based exploitation. 6. Monitor web application logs for unusual or suspicious input patterns that could indicate attempted exploitation. 7. Consider deploying Web Application Firewalls (WAFs) with rules tailored to detect and block XSS attempts targeting ColdFusion applications. 8. Isolate ColdFusion servers from critical internal networks where possible to limit lateral movement if compromised. 9. Maintain an inventory of all ColdFusion instances and versions in use to prioritize patching and risk assessment.