CVE-2024-23330 is a Server-Side Request Forgery (SSRF) vulnerability identified in the Tutanota encrypted email service, specifically affecting versions prior to 119.10. Tutanota is designed to provide secure email communication with privacy protections, including the prevention of automatic loading of external content in emails to avoid leaking user information. However, due to this vulnerability, an attacker can craft an HTML email containing an embedded image that is loaded from an external resource even when the "Automatic Reloading of Images" feature is disabled by default. This unintended behavior causes the Tutanota client to fetch external content unencrypted over HTTP and follow redirections without user consent. The SSRF aspect arises because the email client itself makes the external HTTP requests, potentially exposing internal network details or allowing attackers to probe internal services indirectly. The primary risk is that the sender of the malicious email can detect when the email is opened, identify the device used, and obtain the user's IP address, thereby compromising user privacy and anonymity. This undermines the core privacy guarantees of Tutanota. The vulnerability does not require any user interaction beyond opening the email, and no authentication is needed to exploit it. The issue was addressed in version 119.10 with a patch that prevents automatic loading of external resources without explicit user confirmation. The CVSS v3.1 base score is 5.3 (medium severity), reflecting the network attack vector, low complexity, no privileges or user interaction required, and limited confidentiality impact without integrity or availability compromise.

For European organizations, especially those relying on Tutanota for secure communications, this vulnerability poses a significant privacy risk. The unintended loading of external content can lead to exposure of sensitive metadata such as IP addresses and device information, which can be leveraged for targeted surveillance, profiling, or further attacks. Organizations handling sensitive or regulated data (e.g., GDPR-protected personal data, intellectual property, or confidential communications) may face compliance risks if user privacy is compromised. The SSRF nature of the vulnerability could also be exploited to perform internal network reconnaissance if the email client environment allows access to internal resources, potentially leading to lateral movement or escalation in complex attack scenarios. Since Tutanota is popular among privacy-conscious users and entities in Europe, including NGOs, journalists, and governmental bodies, the impact on confidentiality is particularly critical. However, the vulnerability does not affect message integrity or availability, limiting the scope of damage to privacy breaches rather than data manipulation or service disruption.

European organizations using Tutanota should immediately upgrade all client installations to version 119.10 or later to apply the official patch. Until the upgrade is complete, users should be educated to avoid opening suspicious HTML emails or emails from unknown senders, especially those containing embedded images or external content. Organizations can implement network-level controls to block or monitor outbound HTTP requests from email clients to untrusted external domains, reducing the risk of data leakage. Additionally, configuring email gateways or security appliances to sanitize incoming emails by removing or disabling external content can provide a protective layer. For high-security environments, consider disabling HTML email rendering entirely or using text-only email clients. Regular auditing and monitoring of email client behavior and network traffic can help detect exploitation attempts. Finally, organizations should review their privacy policies and incident response plans to address potential data exposure incidents stemming from this vulnerability.