CVE-2021-40126

CVE-2021-40126 is a medium-severity vulnerability affecting the web-based dashboard of Cisco Umbrella, allowing an authenticated, remote attacker to perform an email enumeration attack. The vulnerability stems from an overly descriptive error message when a user attempts to change their email to one already existing in the system. Exploitation is straightforward, requiring only authenticated access, and could lead to the enumeration of user email addresses within the Umbrella infrastructure. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.