Researchers have just found a flaw within Bitwarden, a popular password manager. If exploited, the bug could give hackers access to login credentials, compromising various accounts.

　　The flaw within Bitwarden was spotted by Flashpoint, a security analysis firm. While the issue hasn’t received much — or any — coverage in the past, it appears that Bitwarden was aware of it all along. Here’s how it works.

　　Image used with permission by copyright holderThe potential security risk lies within Bitwarden’s autofill on page load feature. It lets inline frames (iframes) access your login details, and if said iframes are compromised, then so are your credentials. An iframe is an HTML element that allows developers to embed a different webpage within the page you’re currently on. They’re often used for the purpose of embedding ads, videos, or web analytics.

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　　According to Flashpoint, using Bitwarden with autofill enabled on a page that contains iframes could result in password theft. This is because autofill on page load automatically fills out your login and password both on the page you’re on and within the iframe — and that exposes you to certain risks.

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　　In its report, Flashpoint said: “While the embedded iframe does not have access to any content in the parent page, it can wait for input to the login form and forward the entered credentials to a remote server without further user interaction.”

　　There’s another way hackers could steal your passwords, though. Bitwarden’s autofill on page load also works on subdomains of the domain you’re trying to access, as long as the login matches. This means that if you stumble upon a phishing page, with a subdomain that matches the base domain you’ve saved your password for, Bitwarden might automatically provide it to the hacker.

　　“Some content hosting providers allow hosting arbitrary content under a subdomain of their official domain, which also serves their login page. As an example, should a company have a login page at https://logins.company.tld and allow users to serve content under https://<clientname>.company.tld, these users are able to steal credentials from the Bitwarden extensions,” Flashpoint explained.

　　Andrew Brookes / Getty ImagesThis problem won’t crop up on legitimate, large websites, but free hosting services allow for such domains to be made. Still, both flaws have a pretty small chance of occurring, which is why Bitwarden hasn’t fixed the issue despite being aware of it. In order to keep working on websites that use iframes, Bitwarden has to leave this window of opportunity open for possible phishing and password theft.

　　It’s worth noting that autofill on page load is disabled in Bitwarden by default, and the tool does warn users about the possible risks when they turn the feature on. In response to the report, Bitwarden has said it’s planning an update that will block autofill on subdomains.

　　If you’re not using a tool like Bitwarden yet, make sure to check out our guide to the best password managers. Bitwarden is on that list, and despite this security flaw, it still deserves its place — but perhaps disabling autofill on page load might be a good idea for the time being.