Most users never change defaults. PBKDF2 is thousands of times easier to crack with a GPU than Argon2id. If Bitwarden's servers were breached, vaults using the default KDF would fall first. If you visit a site with a malicious iframe embedded in it, Bitwarden's browser extension may auto-fill your password into the iframe — sending your credentials to the attacker. Bitwarden says this is by design.
What they claim: Bitwarden defaults to PBKDF2-SHA256 with 600,000 iterations for key derivation
What we found: Argon2id is available but not the default — users must manually switch in settings. PBKDF2 is GPU-friendly and significantly weaker against hardware-accelerated attacks compared to Argon2id which is memory-hard. Most users will never change the default.
What they claim: Bitwarden is fully open-source (client and server) under GPL licenses
What we found: CVE-2023-27706: Bitwarden's browser extension auto-filled credentials into embedded iframes, potentially leaking passwords to third-party content on legitimate pages. Bitwarden defended this as a 'design choice' rather than a vulnerability, prioritizing convenience over security.
What they claim: Bitwarden offers self-hosting for complete data sovereignty
What we found: Cloud-hosted vaults (the default for most users) depend on Microsoft Azure infrastructure. While encrypted, the availability and geographic distribution of user vault data is controlled by Azure's infrastructure. Self-hosting requires technical expertise most users don't have.
What they claim: Bitwarden's open-source model allows independent verification of security claims
What we found: CVE-2025-5138: PDF export XSS vulnerability — the initial disclosure went unanswered before being fixed. Response time to security disclosures could be faster for a security-critical product.