# CVE-2021-22538: Privilege escalation in RBAC system

> An attacker with UserWrite permissions can escalate privileges by creating a higher-privileged user due to insufficient permission checks.

- **Severity:** Medium 6.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-5v95-v8c8-3rh6, GO-2022-0798

## What is CVE-2021-22538?

CVE-2021-22538 is a medium-severity vulnerability in Google LLC Exposure Notifications Verification Server, published on 31 Mar 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-276 (Incorrect Default Permissions), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-22538?

3 open source packages ship an affected version, including github.com/google/exposure-notifications-verification-server. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/google/exposure-notifications-verification-server` | Go | All versions | 0.23.1 |
| `github.com/google/exposure-notifications-verification-server` | Go | All versions | 0.23.1 |
| `github.com/google/exposure-notifications-verification-server` | Go | All versions | 0.23.1 |

Products: Google Exposure Notifications Verification Server.

## How do I fix CVE-2021-22538?

Upgrade github.com/google/exposure-notifications-verification-server to 0.23.1 or later.

## Is CVE-2021-22538 being exploited?

There is no known exploitation of CVE-2021-22538 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-22538 and fix it if it is affected.

What it is: CVE-2021-22538 is a medium-severity vulnerability in Google LLC Exposure Notifications Verification Server, published on 31 Mar 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-22538 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/google/exposure-notifications-verification-server (Go): affected all versions; fixed in 0.23.1
- github.com/google/exposure-notifications-verification-server (Go): affected all versions; fixed in 0.23.1
- github.com/google/exposure-notifications-verification-server (Go): affected all versions; fixed in 0.23.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-22538/ (Markdown: https://insights.sbomify.com/CVE-2021-22538/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-22538
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-22538
- OSV: https://osv.dev/vulnerability/CVE-2021-22538

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-22538/
Summaries are generated and may contain mistakes; the official description above is the record.