Digital Wallet

Story: Brevo SSO Flaw Hits 347,000 Trezor Users with Phishing Attack

By Bruce Buterin

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Three Platforms, One Broken System. Trezor moved fast. The company sent warnings to affected subscribers and confirmed that only email…

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Brevo's Authorization Failure. The core problem here is an authorization boundary that didn't hold.

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A login vulnerability in Brevo's system let an attacker blast phishing emails to 347,000 Trezor subscribers. It didn't stop there.

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The attacker's method was pretty simple, which makes it worse. They created a Brevo account, then invited legitimate users into it.

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Because the messages traveled through Brevo's own infrastructure, they passed standard authentication checks without raising flags.

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Trezor moved fast. The company sent warnings to affected subscribers and confirmed that only email addresses were exposed — no additional customer data, no seed phrases, no funds…

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BitBox confirmed the same thing. Its full newsletter and tutorial list went through Brevo, which means every address on it was potentially exposed.

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CoinTracking's situation was slightly different in tone. The platform issued a warning about an email with the subject "Data Breach Notice: Please refresh API Keys as soon as…

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See also: Trezor Users Targeted by Phishing Attack Using Legitimate Email Infrastructure

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The core problem here is an authorization boundary that didn't hold. Brevo's system failed to keep one client's access separate from another's.

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It's murky exactly how that boundary broke down. Brevo acknowledged the breach but hasn't put out a detailed technical explanation.

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That wait is uncomfortable. Email marketing platforms sit at a weird intersection — they hold contact lists for hundreds of clients, process sensitive communications, and act as…

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Crypto users are already primed targets for phishing. Hardware wallet holders especially — attackers know they're likely holding real assets and that a convincing enough scare…

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Related: Anthropics Claude AI Blocks Grant for Controversial Biological Weapons Research

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And the 2,500 users who clicked the link before Trezor disabled it? Unclear what happened to them specifically.

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