Cisco Umbrella Email Enumeration Vulnerability

published 2021-11-04 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-27313

cvss: 4.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.9%; EPSS 0.9% chance of exploitation in 30 days, percentile 59%
public exploits: 0; none known

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.

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2 y ago (2024-11-07)

Exploit prediction

0.87% chance of exploitation in the next 30 days, higher than 59% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD	2.0	4.0	AV:N/AC:L/Au:S/C:P/I:N/A:N

Affected products

Cisco Cisco Umbrella Insights Virtual Appliance

Classification

Weakness

CWE-210 Self-generated Error Message Containing Sensitive Information
CWE-209 Generation of Error Message Containing Sensitive Information

References

tools.cisco.com /security/center/content/CiscoSecurityAdvisory/cisco-sa-umbrella-user-enum-S7XfJwDE
vendor-advisory

Sources

CVE List CVE-2021-40126
NVD CVE-2021-40126

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Summary