Researchers from ETH Zurich have uncovered significant security flaws in several widely used end-to-end encrypted (E2EE) cloud storage platforms, including Sync, pCloud, Seafile, Icedrive, and Tresorit. These vulnerabilities, which range in severity, could allow attackers to access or manipulate sensitive user data by exploiting weaknesses in the providers’ cryptographic designs. The research highlights common failure patterns across independent systems, demonstrating that many of these platforms fail to fully secure the confidentiality and integrity of stored files, despite promising robust encryption.
The identified flaws vary by provider but share troubling characteristics. Sync and pCloud, for example, allow a malicious server to inject files or tamper with existing content, undermining file confidentiality and integrity. Seafile’s vulnerabilities enable faster brute-force attacks on user passwords, while Icedrive’s system allows attackers to compromise file integrity. Tresorit was found to have issues related to presenting non-authentic keys during file-sharing processes. These weaknesses reveal that many E2EE platforms are vulnerable to a malicious server gaining unauthorized access or control, casting doubt on the level of protection these services provide.
ETH Zurich researchers emphasized that these attacks are not particularly complex, making them accessible to attackers with only moderate technical expertise. In many cases, the vulnerabilities stem from basic design flaws, such as the use of unauthenticated keys, weak encryption protocols, and improper handling of metadata. For instance, some platforms were found to use unauthenticated public keys or outdated encryption modes like Cipher Block Chaining (CBC), which are vulnerable to attacks. This means that even users who trust the security claims of E2EE providers could unknowingly be at risk, as these systems fail to meet basic cryptographic standards.
While Sync, Seafile, and Tresorit have acknowledged the report and are working to address the issues, Icedrive has declined to fix the identified vulnerabilities following responsible disclosure in April 2024. The researchers pointed out that the attacks do not require deep cryptographic knowledge, making them a realistic threat to users’ privacy. This discovery underscores the urgent need for cloud storage providers to improve their cryptographic designs and adopt better security practices. With E2EE platforms being trusted by users to protect their most sensitive data, the findings serve as a reminder that robust encryption alone is not enough without thorough security implementation at every level.
