That's even though the patch came out in January, said Kyle Lady, research and development engineer at Duo Security's Duo Labs.
Acccording to Duo's dataset of enterprise Android devices, 80 percent of enterprise phones have the Qualcomm chipset, but only a quarter of them have applied the security update, leaving 60 percent still vulnerable.
In fact, 27 percent are permanently vulnerable, the company said, since they are too old to get the monthly updates.
The vulnerability allows access to Qualcomm Secure Executive Environment, an isolated part of the phone that runs a bare bones operating system that manages encryption keys, protects the hardware, and handles other sensitive operations.
To take over a phone, an attacker first has to convince the user to install malware on the device. That could be via an innocent-looking app that sneaks into the Google Play Store, said Lady.
"Their screening isn't perfect," he said.
Or users could download malicious apps from unofficial sources.
"Consumers want to get the game or whatever, and click and download without considering the security implications," he said.
The attacker would then use the Qualcomm vulnerability in combination with an existing media server vulnerability to get into the phone's secure area.
It doesn't need to be a newly-discovered media server vulnerability either, Lady added.
"Given how many phones don't get regular updates, there's no reason to use a new one, when you can just use an old one," he said.
The media server has special permissions to communicate with the Qualcomm Secure Executive Environment, and "critical" and "high" severity vulnerabilities are common. For example, there were seven in May's security bulletin and 11 in April's, according to Duo.
The QSEE vulnerability was first described by Gal Beniamini in the Bits, Please! blog.
It is based on a security hole in one of the QSEE's trusted applications, the one that manages encryption keys for Widevine's DRM software.
There's little that enterprises can do to protect against this exploit, Lady said.
"There really isn't any way for them to force a patch to happen," he said. "If it isn't a Nexus phone, the manufacturer has to apply the patch to the software, then send it to the carrier, such as Verizon. The carrier has to approve it, and then send it to customers using that phone. So there's a substantial delay."
Nexus phones get automatic updates from Google, Lady said.
However, companies can warn employees not to download software from unofficial sources, or use a mobile device management tool to restrict what employees can install on company-provided phones.
"Though there are many workarounds to those policies," he added.
Companies can also use a solution that checks whether devices have all their patches up-to-date, and put additional access controls around those that don't.
What really needs to happen is that the Android update and patching system needs to change, Lady said.
Or companies can switch to Nexus phones, he added.