How severe is CVE-2021-22538?

CVE-2021-22538 has a CVSS score of 8.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-22538?

CVE-2021-22538 affects the following packages: github.com/google/exposure-notifications-verification-server (Go). Ecosystems affected: Go.

How do I fix CVE-2021-22538?

Update github.com/google/exposure-notifications-verification-server to 0.23.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-22538 is resolved across your whole dependency graph.

How do I detect CVE-2021-22538 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/google/exposure-notifications-verification-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-22538 if there is no patch (or I can't update yet)?

Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Is CVE-2021-22538 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-22538 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-22538?

CVE-2021-22538 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 52th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-22538?

CVE-2021-22538 is classified as Improper Input Validation (CWE-20), Incorrect Default Permissions (CWE-276). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-22538 published, and has it been updated?

CVE-2021-22538 was published on March 31, 2021 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2021-22538 — exposure-notifications-ve…

HIGHFix: google/exposure-notifications-verification-server@eb8cf40

CVE-2021-22538 is a high-severity (CVSS 8.8) Improper Input Validation vulnerability in github.com/google/exposure-notifications-verification-server. A fix is available for github.com/google/exposure-notifications-verification-server — see the affected versions and patch details below.

Privilege escalation in rbac

Also known asGHSA-5v95-v8c8-3rh6GO-2022-0798

Published

Mar 31, 2021

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs52th percentile — riskier than 52% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-22538 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/google/exposure-notifications-verification-server

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Using a carefully crafted request or malicious proxy, a user with UserWrite permissions could create another user with higher privileges than their own due to insufficient checks on the allowed set of permissions. The event would be captured in the Event Log.

Patches

The issue has been fixed in 0.24.0 and 0.23.1.

Workarounds

For users who are unable to upgrade, we recommend auditing users who have UserWrite permissions and regularly reviewing the Event Log for malicious activity.

Kudos

Thank you to Michael Mazzolini (Ethical Hacker at WHO) for finding and disclosing this vulnerability.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/google/exposure-notifications-verification-server`	all versions	0.23.1`go get github.com/google/exposure-notifications-verification-server@v0.23.1`

Affected Products

1 product · 1 configurations

Application

exposure notifications verification servergoogle

< 0.23.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/google/exposure-notifications-verification-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/google/exposure-notifications-verification-server to 0.23.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-22538 is resolved across your whole dependency graph.
Workarounds
Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Frequently Asked Questions

### Impact Using a carefully crafted request or malicious proxy, a user with `UserWrite` permissions could create another user with higher privileges than their own due to insufficient checks on the allowed set of permissions. The event would be captured in the Event Log. ### Patches The issue has been fixed in 0.24.0 and 0.23.1. ### Workarounds For users who are unable to upgrade, we recommend auditing users who have `UserWrite` permissions and regularly reviewing the Event Log for malicious activity. ### Kudos Thank you to Michael Mazzolini (Ethical Hacker at WHO) for finding and disclosi