Cloud-based password managers promise that not even their operators can read what users store, but researchers in ETH Zurich's Applied Cryptography Group, Matilda Backendal, Matteo Scarlata, Giovanni Torrisi and professor Kenneth Paterson, found that the promise does not hold. Examining Bitwarden, LastPass and Dashlane, which together serve about 60 million users, they demonstrated 25 distinct attacks: 12 against Bitwarden, 7 against LastPass and 6 against Dashlane.
The team built servers that mimic a compromised provider and assumed a malicious server behaving unpredictably towards client software, a realistic threat after a breach or insider attack. In most cases they could view and even alter stored passwords, with some attacks escalating from individual vaults to every vault in an organisation, triggered by routine actions such as logging in, opening a vault or syncing data. Many providers still rely on cryptographic methods dating from the 1990s.
The researchers disclosed the flaws to all three companies 90 days before publication and recommend adopting current cryptographic standards, at least for new customers, and communicating security guarantees more honestly. The study, available as a preprint ahead of USENIX Security 2026, is a reminder that users should favour services that undergo external audits, are open about vulnerabilities and enable end-to-end encryption by default.