What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-03-26 · updated 2026-06-17
• Weakness: CWE-200

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.

Affected products

• wireapp wire-server: from 2021-02-16 before 2021-03-02 — fixed in 2021-03-02

How to fix

Upgrade to a fixed version: wireapp wire-server 2021-03-02. Check the vendor advisory for mitigations.

References

• https://github.com/wireapp/wire-server/commit/7ba2bf4140282557cf215e0b2c354d4d08cd3421
• https://github.com/wireapp/wire-server/releases/tag/v2021-03-02
• https://github.com/wireapp/wire-server/security/advisories/GHSA-qx8q-rhq2-rg4j
• https://github.com/wireapp/wire-server/commit/7ba2bf4140282557cf215e0b2c354d4d08cd3421
• https://github.com/wireapp/wire-server/releases/tag/v2021-03-02
• https://github.com/wireapp/wire-server/security/advisories/GHSA-qx8q-rhq2-rg4j

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