CVE-2024-45516 is a Cross-Site Scripting (XSS) vulnerability affecting multiple versions of Zimbra Collaboration Suite (ZCS), specifically versions 9.0.0 prior to Patch 43, 10.0.x prior to 10.0.12, 10.1.x prior to 10.1.4, and 8.8.15 prior to Patch 47. The vulnerability resides in the Classic UI of Zimbra, where insufficient sanitization of HTML content allows attackers to embed malicious JavaScript code within malformed <img> tags. When a user views a specially crafted email containing such malicious content in the Classic UI, the embedded JavaScript executes within the context of the user's session. This can lead to unauthorized access to sensitive information, session hijacking, or other malicious actions that leverage the user's authenticated session. The attack requires no additional user interaction beyond viewing the email, making it a low-barrier exploit. The CVSS 3.1 base score is 6.1 (medium severity), with an attack vector of network (remote), low attack complexity, no privileges required, but user interaction is needed (viewing the email). The scope is changed, indicating that the vulnerability affects components beyond the initially vulnerable component, and the impact affects confidentiality and integrity but not availability. No known exploits are currently reported in the wild, and no official patches are linked in the provided data, though patches exist for the affected versions as indicated by the version numbers. The root cause is a classic CWE-79 (Improper Neutralization of Input During Web Page Generation) issue, common in web applications that fail to sanitize user-supplied input properly.

For European organizations using Zimbra Collaboration Suite, this vulnerability poses a significant risk to the confidentiality and integrity of email communications. Since Zimbra is widely used in enterprise and government sectors for email and collaboration, exploitation could lead to unauthorized disclosure of sensitive corporate or personal data, including internal communications, credentials, or confidential attachments. The ability to execute arbitrary JavaScript within a user's session could also facilitate session hijacking or further phishing attacks, potentially enabling attackers to escalate privileges or move laterally within an organization's network. Given that the vulnerability requires only that a user open a malicious email, the attack surface is broad, especially in organizations with large user bases. The impact is heightened in sectors with strict data protection regulations such as GDPR, where data breaches can lead to significant legal and financial penalties. Additionally, the compromise of email accounts can undermine trust in communication channels and disrupt business operations.

European organizations should prioritize applying the latest security patches provided by Zimbra for the affected versions (Patch 43 for 9.0.0, 10.0.12 for 10.0.x, 10.1.4 for 10.1.x, and Patch 47 for 8.8.15). In the absence of immediate patching, organizations should consider disabling or restricting access to the Classic UI, encouraging users to switch to the newer Zimbra UI versions if they are not vulnerable. Implementing robust email filtering solutions that detect and quarantine emails containing suspicious or malformed HTML content can reduce the risk of malicious emails reaching end users. User education campaigns should emphasize caution when opening unexpected or suspicious emails, even from known contacts. Additionally, deploying Content Security Policy (CSP) headers and other browser-based mitigations can help limit the impact of XSS attacks. Monitoring email logs and user activity for unusual behavior indicative of exploitation attempts is also recommended. Finally, organizations should review and harden their web application firewall (WAF) rules to detect and block XSS payloads targeting Zimbra interfaces.