This is a plausible scenario in the case of sophisticated hackers or nation-state actors. The researchers found that while these platforms promise airtight security and privacy through their E2EE models, their real-world implementation may fall short of these claims.
Sync, for instance, exhibited critical vulnerabilities due to unauthenticated key material, which allows attackers to introduce their own encryption keys and compromise data. It was found that shared files could be decrypted, and passwords were inadvertently exposed to the server, compromising confidentiality. Attackers could also rename files, move them undetected, and inject folders into user storage.
pCloud’s flaws were similar, with attackers able to overwrite private keys, effectively forcing encryption using attacker-controlled keys.
This, coupled with public keys that were unauthenticated, granted attackers access to encrypted files. Attackers could also alter metadata, such as file size, reorder file chunks, or even inject files.
Icedrive was shown to be vulnerable to file tampering due to its use of unauthenticated CBC encryption. Attackers could modify the contents of files, truncate file names, and manipulate file chunks, all without detection.
Seafile also presented several serious vulnerabilities, including susceptibility to protocol downgrade attacks, which made brute-forcing passwords easier. The encryption used by Seafile was not authenticated, enabling file tampering and manipulation of file chunks. As with other platforms, attackers could inject files or folders into a user’s storage space.
Tresorit fared slightly better than its peers, but still had issues with public key authentication, where attackers could potentially replace server-controlled certificates to gain access to shared files. While Tresorit’s flaws didn’t allow direct data manipulation, some metadata was still vulnerable to tampering.
The vulnerabilities discovered by the ETH Zurich researchers call into question the marketing promises made by these platforms, which often advertise their services as providing the highest level of security and privacy through end-to-end encryption. In light of these findings, users are advised to exercise caution when trusting these platforms with sensitive data, particularly in cases where the server is compromised.
The researchers notified Sync, pCloud, Seafile, and Icedrive of their findings in April 2024, while Tresorit was informed in late September 2024. Responses from the vendors varied. Icedrive declined to address the issues, Sync is fast-tracking fixes, and Tresorit is working on future improvements to further safeguard user data. Seafile has promised to patch specific vulnerabilities, while pCloud had not responded as of October 2024.
While no evidence suggests that these vulnerabilities have been exploited, the flaws are nonetheless concerning for users who rely on these platforms for storing sensitive data.
The findings also emphasize the need for ongoing scrutiny and improvement of encryption protocols and security features in cloud storage solutions, as even end-to-end encryption does not guarantee absolute protection without proper implementation.
As more people rely on cloud storage for personal and professional use, these discoveries are a reminder of the importance of choosing platforms that prioritize transparent, verifiable security measures.
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