Is CVE-2021-40126 actively exploited?

No active exploitation of CVE-2021-40126 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-40126 be exploited remotely?

Yes. CVE-2021-40126 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-40126?

CVE-2021-40126 has a CVSS score of 4.3 (MEDIUM).

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MEDIUM

CVE-2021-40126

CWE-210Published: November 4, 2021· Updated: Jun 17, 2026

4.3

CVSS v3.1

Official Description

A vulnerability in the web-based dashboard of Cisco Umbrella could allow an authenticated, remote attacker to perform an email enumeration attack against the Umbrella infrastructure. This vulnerability is due to an overly descriptive error message on the dashboard that appears when a user attempts to modify their email address when the new address already exists in the system. An attacker could exploit this vulnerability by attempting to modify the user's email address. A successful exploit could allow the attacker to enumerate email addresses of users in the system.

NVD Source

Technical Analysis

CVE-2021-40126 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.