# CVE-2021-21396: Bulk list client endpoint exposes too much metadata about a client

> Logged-in users can access sensitive client metadata of other users via an exposed endpoint, requiring an upgrade to the Wire backend server.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-qx8q-rhq2-rg4j

## What is CVE-2021-21396?

CVE-2021-21396 is a medium-severity vulnerability in wireapp wire-server, published on 26 Mar 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

wire-server is an open-source back end for Wire, a secure collaboration platform. In wire-server from version 2021-02-16 and before version 2021-03-02, the client metadata of all users was exposed in the `GET /users/list-clients` endpoint. The endpoint could be used by any logged in user who could request client details of any other user (no connection required) as far as they can find their User ID. The exposed metadata included id, class, type, location, time, and cookie. A user on a Wire backend could use this endpoint to find registration time and location for each device for a given list of users. As a workaround, remove `/list-clients` from nginx config. This has been fixed in version 2021-03-02.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2021-21396?

It affects 1 product.


Products: Wire Wire Server.

## How do I fix CVE-2021-21396?

No fix has been published for CVE-2021-21396 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21396 being exploited?

There is no known exploitation of CVE-2021-21396 in the wild and no public exploit code.

## Other vulnerabilities in wireapp wire-server

- [CVE-2022-31122](https://insights.sbomify.com/CVE-2022-31122/): Auth bypass in wire-server (critical 9.8)
- [CVE-2021-41101](https://insights.sbomify.com/CVE-2021-41101/): CORS `Access-Control-Allow-Origin` settings are too lenient (medium 5.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21396 and fix it if it is affected.

What it is: CVE-2021-21396 is a medium-severity vulnerability in wireapp wire-server, published on 26 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-2021-21396 in the wild and no public exploit code.

Affected product: wireapp wire-server. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-21396/ (Markdown: https://insights.sbomify.com/CVE-2021-21396/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21396
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21396
- OSV: https://osv.dev/vulnerability/CVE-2021-21396

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21396/
Summaries are generated and may contain mistakes; the official description above is the record.