How severe is CVE-2021-40126?

CVE-2021-40126 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2021-40126 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40126?

CVE-2021-40126 affects Cisco Umbrella. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40126?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-40126 published?

CVE-2021-40126 was published on 2021-11-04 and last updated on 2026-06-17.

CVE-2021-40126

CVE-2021-40126 is a medium-severity vulnerability in Cisco Umbrella with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-209.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
CVSS v2: 4.0
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-209
Affected product: Cisco Umbrella
Published: 2021-11-04
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-40126?: 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.
How severe is CVE-2021-40126?: CVE-2021-40126 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2021-40126 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40126?: CVE-2021-40126 affects Cisco Umbrella. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40126?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-40126 published?: CVE-2021-40126 was published on 2021-11-04 and last updated on 2026-06-17.

References

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-umbrella-user-enum-S7XfJwDE

Affected products (1)

cpe:2.3:a:cisco:umbrella:-:*:*:*:*:*:*:*

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