The average company's network is accessed by 89 different vendors every week, according to a new research report that surveyed more than 600 IT decision makers at mid-sized and large enterprises - but only a third were confident that they knew the exact number of vendors who had accessed their systems.
And the number of partners, vendors, contractors and temporary workers who require access is only increasing, said Matt Dircks, CEO at Bomgar, which sponsored the research.
Three quarters of those polled stated the number of third-party vendors used by their organisation has increased in the last two years, and 71 per cent believe the numbers will continue to increase in the next two years.
"It's becoming an exponentially contentious problem," he said. "A perfect storm."
It's not that companies aren't aware of the potential risks, he added.
In fact, 81 per cent of respondents admitted that high profile data breaches, such as the 2013 attack on Target, have increased their awareness of the need for better third-party vendor controls. Yet only a third (35 per cent) are confident they know the exact number of vendors accessing their IT systems.
In addition, while 56 per cent of companies have some degree of ability to track or limit what outsiders are doing on their networks, 44 per cent have an all-or-nothing approach to vendor access management.
As a result, while 92 per cent said they trust vendors completely or most of the time, two-thirds admitted that they tend to trust vendors too much, and 69 per cent reported that they had definitely or possibly suffered a security breach resulting from vendor access in the past year.
And 77 per cent of respondents said they expect to have a breach within the next two years based on the vendors in their networks.
"I was surprised," Dircks said.
The risks are likely to increase, he added, as a result of the growth of the Internet of Things and of sub-contractors.
Survey respondents agreed - 74 per cent said they were concerned about IT breaches originating from connected devices during the next year and 72 per cent see vendors using their own sub-contractors as a further risk.
According to Bomgar, two main factors are contributing to the lack of oversight of vendor access.
One is the difficulty of keeping up with the changing cyberthreat landscape and making sure all their third-party access policies and up-to-date and adequately enforced.
More than half of those surveyed have not reviewed their policy around third-party access in the last two years, and only 51 per cent said they enforce policies around third-party access.
The other side of the coin is the vendor selection process itself.
More than half of respondents said that threats related to vendor access were not taken seriously enough in their organization, nearly three quarters said that third-party vendor selection overlooks key risks, and 64 per cent said that their organisation focuses more on cost than security.