Researchers from ETH Zurich have uncovered 25 serious vulnerabilities in three leading cloud-based password managers: Bitwarden, LastPass, and Dashlane.

These flaws enable a malicious server to bypass zero-knowledge encryption claims, allowing unauthorized access, modification, and recovery of users’ stored passwords and vault data.

Bitwarden, LastPass, and Dashlane collectively serve over 60 million users and hold significant market share. The analysis targets their client-server interactions under a fully malicious server threat model, where servers deviate arbitrarily from protocols.

Vendors advertise “zero-knowledge encryption,” implying servers cannot access plaintext vaults even if compromised, but the researchers demonstrate repeated failures in confidentiality and integrity protections.

The 25 attacks span four categories: key escrow mechanisms, item-level vault encryption flaws, sharing features, and backwards compatibility issues.

Key Escrow Attacks

These target account recovery and SSO login mechanisms enable full vault compromise via unauthenticated keys. Bitwarden’s BW01-BW03 allow malicious auto-enrollment, key rotation, and KC conversion through key substitution upon joining organizations or dialogs. LastPass’s LP01 exploits password reset flaws similarly.

Item-Level Encryption Flaws

Flawed per-item encryption leads to integrity violations, metadata leaks, field swapping, and KDF downgrades. Bitwarden’s BW04-BW07 expose unprotected metadata, swap fields, decrypt icons, and remove iterations for brute-force. LastPass LP02-LP06 and Dashlane DL01 enable malleable vaults and replay attacks due to AES-CBC and missing bindings.

Unauthenticated public keys compromise organizations and shared vaults. Bitwarden’s BW08-BW09 inject or overwrite organizations; LastPass LP07 and Dashlane DL02 overwrite sharing keys upon joining. Impacts scale to team-wide access.

Backwards Compatibility Issues

Legacy code support triggers downgrades to insecure modes like CBC. Bitwarden’s BW10-BW12 disable protections and overwrite keys; Dashlane’s DL03-DL06 enable injections, KDF removal, and “Lucky 64” after syncs. Dashlane patched via extension 6.2544.1.

In Bitwarden, 12 attacks include malicious auto-enrollment (BW01), where unauthenticated organization public keys allow key substitution and full vault compromise upon joining any group.

LastPass faces seven issues, such as lacking ciphertext integrity with AES-CBC (LP05), enabling malleable vaults, and field swapping. Dashlane has six vulnerabilities, like transaction replay (DL01) due to shared keys across transactions, violating vault integrity.

Attack Ref	Product	Cause	Impact	Client Interaction
BW01	Bitwarden	Lack of Key Auth, Key Substitution	Full vault compromise	1 join
BW02	Bitwarden	Key Substitution	Full vault compromise	1 rotation
BW03	Bitwarden	Lack of Key Auth, Key Substitution	Full vault compromise	1 dialog
LP01	LastPass	Lack of Key Auth	Full vault compromise	1 login
BW04	Bitwarden	Lack of Auth Enc	Read/modify metadata	–
BW05	Bitwarden	Lack of Key Sep	Field/item swapping	–
BW06	Bitwarden	Lack of Key Sep	Loss of confidentiality	1 open
BW07	Bitwarden	Lack of Auth Enc	No brute-force protection	1 login
LP02	LastPass	Lack of Auth Enc	Field/item swapping	–
LP03	LastPass	Lack of Key Sep	Loss of confidentiality	1 open
LP04	LastPass	Lack of Auth Enc	No brute-force protection	1 login
LP05	LastPass	Lack of Auth Enc	Loss of vault integrity	–
DL01	Dashlane	Lack of Key Sep	Loss of vault integrity	–
BW08	Bitwarden	Lack of Key Auth	Add users to orgs	1 sync
BW09	Bitwarden	Lack of Key Auth, Key Substitution	Org compromise	1 join
LP07	LastPass	Lack of Key Auth	Shared vault compromise	1 join
DL02	Dashlane	Lack of Key Auth	Shared vault compromise	1 join
BW10	Bitwarden	Lack of Auth Enc	Downgrade key hierarchy	–
BW11	Bitwarden	CBC Support	Loss of confidentiality	2 logins
BW12	Bitwarden	CBC Support	Full vault compromise	2 logins
DL03	Dashlane	CBC Support	Loss of vault integrity	104 syncs
DL04	Dashlane	CBC Support	No brute-force protection	104 syncs
DL05	Dashlane	CBC Support	Loss of confidentiality	105 syncs
DL06	Dashlane	CBC Support	No brute-force protection	104 syncs
LP06	LastPass	Lack of Auth Enc	Read/modify metadata	–

Many attacks require minimal interaction, like a single login or sync, exploiting unauthenticated public keys, missing key separation, and legacy AES-CBC support. For instance, icon URL decryption leaks (BW06, LP03) reveal passwords via client requests. KDF iteration downgrades (BW07, LP04) accelerate brute-force by up to 300,000x.

Researchers disclosed findings responsibly: Bitwarden on January 27, 2025; LastPass on June 4, 2025; Dashlane on August 29, 2025, with 90-day remediation windows.

Bitwarden advanced fixes for several, including minimum KDF iterations and CBC removal; LastPass addressed LP03; Dashlane mitigated some CBC issues. Recommended mitigations include authenticated encryption (AE), full key separation (KS), public key authentication (PKA), and ciphertext signing (SC).

Users should update clients, enable per-item keys where available, and monitor vendor patches. The study urges formal security models for password managers akin to E2EE cloud storage. Self-hosted deployments remain vulnerable if servers are compromised.

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