The problem was uncovered by the Project Zero team at Google. Introduced as part of the Windows 10 1903 update on May 21 of last year, the mistake reveals the catastrophic effects a single line of code can have (via BleepingComputer).
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The vulnerability in question, identified as CVE-2020-0981 (opens in new tab), was fixed as part of an April 2020 update to Windows 10, but it’s an instructive look at how easily security measures can break down as a result of even minor changes across the myriad lines of code in Windows 10. Here’s the original line of code: NewToken->ParentTokenId = OldToken->TokenId; And the Windows 10 1903 update to the code: NewToken->ParentTokenId = OldToken->ParentTokenId; The change in question created a token security feature bypass that Chromium was dependant on to maintain its secure sandbox. Rather than limiting new sandboxed processes to Restricted Tokens, it allowed a new sandboxed process to have a token that could be “considered a sibling of any other token on the desktop.” This fundamental break in a core Windows 10 security feature that the Chromium team was building off of, allowed Project Zero security researcher, James Forshaw, to create a complicated chain of events that exploited multiple Windows 10 vulnerabilities and would have allowed an attacker to escape the secure Chromium sandbox. This is the diagram of Mr. Forshaw’s exploit, just to give you an idea of the complexity. If you want to read the technical breakdown of the flaw along with Mr. Forshaw’s full description of his sandbox escape method, you can read his account on the Google Project Zero blog.
