(Image: CNET/CBS Interactive)

Just hours before Apple is expected to roll out the new version of its desktop and notebook operating system, macOS High Sierra, a security researcher dropped a zero-day.

Patrick Wardle, a former NSA hacker who now serves as chief security researcher at ‎Synack, posted a video of the hack -- a password exfiltration exploit -- in action.

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Passwords are stored in the Mac's Keychain, which typically requires a master login password to access the vault.

But Wardle has shown that the vulnerability allows an attacker to grab and steal every password in plain-text using an unsigned app downloaded from the internet, without needing that password.

Wardle tested the exploit on High Sierra, but said that older versions of macOS and OS X are also vulnerable.

He tweeted a short video demonstrating the hack.

Wardle created a "keychainStealer" app demonstrating a local exploit for the vulnerability, which according to the video, can expose passwords to websites, services, and credit card numbers when a user is logged in.

That exploit could be included in a legitimate-looking app, or be sent by email.

"If I was an attacker or designing a macOS implant, this would be the 'dump keychain' plugin," said Wardle.

He reported the bug to Apple earlier this month, "but unfortunately the patch didn't make it into High Sierra," he said, which was released Monday.

"As a passionate Mac user, I'm continually disappointed in the security of macOS," he said. "I don't mean that to be taken personally by anybody at Apple -- but every time I look at macOS the wrong way something falls over. I felt that users should be aware of the risks that are out there I'm sure sophisticated attackers have similar capabilities."

"Apple marketing has done a great job convincing people that macOS is secure, and I think that this is rather irresponsible and leads to issues where Mac users are overconfident and thus more vulnerable," he added.

In his tweet, Wardle suggested that Apple should launch a macOS bug bounty program "for charity." Right now, Apple only has a bug bounty for iPhones and iPads, which pays up to $200,000 for high-end secure boot firmware exploits.

It's the second zero-day that Wardle found for the operating system this month -- the first shows how the new software's secure kernel extension loading feature is vulnerable to bypass.

Apple provided sister-site CNET with a statement, after publication:

"MacOS is designed to be secure by default, and Gatekeeper warns users against installing unsigned apps, like the one shown in this proof of concept, and prevents them from launching the app without explicit approval. We encourage users to download software only from trusted sources like the Mac App Store, and to pay careful attention to security dialogs that macOS presents."

Apple did not say if or when it will patch the bug.