CVE-2021-22538

Name: CVE-2021-22538
Creator: NVD / NIST
Published: 2021-03-31T21:15:16.057+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.8/10EPSS 0.72%

Last modified Jun 17, 2026

CVE-2021-22538 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. A privilege escalation vulnerability impacting the Google Exposure Notification Verification Server (versions prior to 0.23.1), allows an attacker who (1) has UserWrite permissions and (2) is using a carefully crafted request or malicious proxy, to create another user with higher privileges than their own. This occurs due to insufficient checks on the allowed set of permissions. EPSS estimates a 0.72% chance of exploitation in the next 30 days.

Description

A privilege escalation vulnerability impacting the Google Exposure Notification Verification Server (versions prior to 0.23.1), allows an attacker who (1) has UserWrite permissions and (2) is using a carefully crafted request or malicious proxy, to create another user with higher privileges than their own. This occurs due to insufficient checks on the allowed set of permissions. The new user creation event would be captured in the Event Log.

Metrics

CVSS 3.1

8.8/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.72%

49.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Google	Exposure Notifications Verification Server	< 0.23.1

References

https://github.com/google/exposure-notifications-verification-server/commit/eb8cf40b12dbe79304f1133c06fb73419383cd95Patch, Third Party Advisory
https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.23.1Release Notes, Third Party Advisory
https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.24.0Release Notes, Third Party Advisory
https://github.com/google/exposure-notifications-verification-server/security/advisories/GHSA-5v95-v8c8-3rh6Third Party Advisory
https://github.com/google/exposure-notifications-verification-server/commit/eb8cf40b12dbe79304f1133c06fb73419383cd95Patch, Third Party Advisory
https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.23.1Release Notes, Third Party Advisory
https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.24.0Release Notes, Third Party Advisory
https://github.com/google/exposure-notifications-verification-server/security/advisories/GHSA-5v95-v8c8-3rh6Third Party Advisory

Timeline

Published: Mar 31, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-22538?

How severe is CVE-2021-22538?

CVE-2021-22538 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 0.72% probability of exploitation in the next 30 days.

How do I fix CVE-2021-22538?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-22538?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST