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In June 2022, security researchers from SonarSource discovered a critical Cross-Site Scripting (XSS) vulnerability in the open-source code of Proton Mail. This flaw could have allowed attackers to bypass end-to-end encryption to steal decrypted emails and impersonate victims. The Discovery
If successful, the script would run in the victim's session, allowing the attacker to "see" what the user sees—effectively stealing the decrypted content of their inbox. Proton's Response and Resolution
The Sonar Research team identified the vulnerability during a routine audit of Proton's open-source repositories. The issue stemmed from how the web application handled user-controlled HTML. While senders need the ability to style messages, failing to properly sanitize certain tags can allow malicious tags to execute in a reader's browser. How the Exploit Worked Proton Exploit
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After researchers disclosed the bug in June 2022, Proton developed and deployed a fix by early July 2022. Proton's Response and Resolution The Sonar Research team
In most scenarios, the attack only worked if the victim viewed both emails and clicked a specific link in the second one.
The vulnerability was strictly limited to the web interface; non-web Proton Mail apps (iOS/Android) were never affected. Protecting Your Data How the Exploit Worked Shift the tone (e
Add details about other recent fixes (like the patch). Include SEO keywords tailored for cybersecurity audiences. Proton Mail's responsible vulnerability disclosure policy