Sideloaded extensions are particularly vulnerable: After confirming the behavior on VSCode, OX extended their investigation to other platforms, including Visual Studio, IntelliJ IDEA, and Cursor.The researchers said that despite the differences in file structures and verification mechanisms across platforms, they were able to identify the requests used for verification and locate the relevant values within the extensions. They added that by modifying these values, they successfully created extensions that retained their verified status.According to OX Security, when it informed Microsoft about the verification flaw, Microsoft responded by saying, “After careful investigation, this case has been assessed as by design and does not meet Microsoft’s bar for immediate servicing. This is as designed. Furthermore, the changes will be prevented by extension signature verification, now enabled by default across all platforms. The attacker will be unable to publish this to the Marketplace, so only side-loading is possible.”Microsoft further told OX Security that a dedicated team is working on additional actions to keep customers protected. However, OX Security found the flaw still exploitable on June 29, 2025. Other vendors echoed Microsoft’s stance on the disclosure. JetBrains (IntelliJ IDEA) told OX Security that since the plugin in question doesn’t originate from the JetBrains Marketplace, it is treated as a third-party, unverified extension, which the platform explicitly flags to users before installation. Cursor, meanwhile, told OX Security that it does not continuously verify extensions once they are installed.
First seen on csoonline.com
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