And this percentage rose to 95% when one considered only the browsers made by Microsoft, the company said in its annual evaluation of flaws in software made by the Redmond behemoth.
Despite claims being made about improved security in Windows 10, it was found that the number of flaws in this version rose by 64% in 2017. As with all other Microsoft products, removing admin rights would mitigate almost 80% of these flaws.
Avecto makes privilege management and application control software and has been issuing these evaluations since 2013. The figures are all taken from the security bulletins issued by Microsoft throughout the year.
Avecto found a 54% increase in the number of critical Microsoft vulnerabilities since 2016; that figure was 60% if one took the whole five-period into account.
The browsers made by Microsoft showed an increase in vulnerabilities since 2013, with Avecto registering a rise of 46%.
Clarifying its findings, Avecto said: "Security vulnerability and update information issued by Microsoft contains a summary with general information regarding that vulnerability.
"For this report, a vulnerability is classed as one that could be mitigated by removing admin rights if the sentence 'Customers/users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights' or 'If the current user is logged on with administrative user rights, an attacker could take control of an affected system' is found within the summary of that specific vulnerability."
In its report, Avecto classifies vulnerabilities into categories: remote code execution, elevation of privilege, information disclosure, denial of service, security feature bypass, spoofing and tampering.
In 2017, there were 587 vulnerabilities found across Windows Vista, Windows 7, Windows RT, Windows 8/8.1 and Windows 10.
"This is a record high, coming in 232 vulnerabilities more than last year's report, and marking a 132% increase from five years ago," the report said.
There were 48 critical flaws found in Internet Explorer (versions 8 to 11) in 2017 and 45 of these could have been mitigated by the removal of admin rights.
As far as Edge was concerned, 140 critical vulnerabilities were found in 2017, a rise of 140% since the browser made its debut two years ago. All but six of these could have been mitigated by removing admin rights.
Microsoft Office vulnerabilities also continued to show a year-on-year rise, hitting a record high of 87 in 2017. Critical vulnerabilities had doubled compared to 2013, though the numbers were small – from 6 to 12.
Sixty percent of the vulnerabilities in all Office components (Excel, Word, PowerPoint, Visio, Publisher and others) would have been mitigated by the removal of admin rights.
Windows Server had a total of 501 vulnerabilities in 2017 with Microsoft grading 176 of these as critical. Avecto said 74% could be mitigated by the removal of admin rights. Flaws doubled over the five years from 2013, when 252 were found, with the biggest rise being this year, a 65% increase over the 303 found in 2016.
Commenting on Avecto's findings, Jake Williams, the head of security firm Rendition Infosec, said: "“Removing admin rights from your users is one of the most important things you can do to mitigate vulnerabilities. Some organisations believe that user account control will protect them, but attackers know of many methods to silently bypass UAC popups."
Williams, a former member of the NSA's elite Tailored Access Operations hacking unit, added: "Even Microsoft says that UAC is not a security control. By removing administrative rights from your users, you ensure that the attacker cannot take full control of a machine even if a vulnerability is exploited."
The Avecto report is available here as a free download after registration.