Security researchers chained together five separate weaknesses in the popular workflow automation service Zapier that, if first discovered by a malicious actor, could have granted access to millions of user accounts and the systems those accounts connect to.

The flaws, disclosed by security firm Token Security, did not require malware or insider access. The only prerequisite, according to the company’s report, was a free Zapier account. From there, researchers chained together weaknesses that, if taken individually, would have looked routine, but together opened a path to one of the most widely used services of the modern internet.

Zapier’s software can be configured to move data between email, customer-relationship tools, payment processors, calendars, code repositories and thousands of other applications. The company says it supports more than 8,000 third-party integrations and has millions of users, which means breaking into Zapier could escalate into a wide-ranging supply-chain attack.

The researchers said an attempted attack would start by exploiting a weakness in how users write small pieces of code as part of their automations. Once that feature was isolated, researchers recovered login credentials the service had tried to discard. Those credentials, in turn, exposed an internal storage system holding more than 1,100 of Zapier’s private software images, one of which contained a publishing key for a piece of code that runs inside every logged-in Zapier user’s browser.

According to the report, if an attacker updated that code, they could have acted as a legitimate user inside the platform, creating new automations, altering existing ones, and tapping into connections the user had already approved to outside services. From there, they could instruct the platform to send emails, move files, pull records from customer databases, or post messages, all from accounts that appeared entirely legitimate.

The researchers stressed that a possible attacker could not have obtained passwords or login keys for those connected services, as those remain on Zapier’s servers. But because the actions would have been carried out through Zapier itself, they would have looked, to any outside system, like the user’s own.

A separate finding, uncovered during the same research, illustrated how immediate that risk can be. The researchers said they discovered a working key tied to the personal account of the chief technology officer of an outside artificial-intelligence company whose software Zapier used internally. Using that key, they were able to send an email from the executive’s own Gmail account to a mailbox they controlled.

Token Security told Zapier the capability existed but did not exploit it. The researchers confirmed they had the access needed to push a malicious update into code running inside every signed-in Zapier user’s browser, and instead reported the findings in February under the company’s bug-bounty program. 

Researchers said that Zapier triaged the issues within four days, remediated within three weeks, and worked with the company to allow disclosure. The company paid the program’s maximum bounty of $3,000 and says it has no evidence the weaknesses were exploited before they were patched.

“Worth saying out loud in a culture that often punishes disclosure programs for slowness,” Token’s blog post reads.  

Zapier did not respond to CyberScoop’s request for comment. 

The episode lands at a moment when automation platforms and artificial-intelligence tools are increasingly being granted the standing authority to act on behalf of users across dozens of services at once. Token Security’s researchers argued that the weaknesses they found were not unique to Zapier. Each link in the chain, they said, was a well-documented kind of mistake. The vulnerability was the chain itself, and the same pattern, they warned, almost certainly exists at other companies that have not yet looked.

Zapier says the issues have been fixed and no further action is required. But the researchers suggested organizations with heightened sensitivity review their automation logs for anything they did not create, and consider reauthorizing Zapier connections to particularly sensitive systems.

You can read the full research report on Token Security’s website.