CVE-2023-5333 Denial of Service via multiple identical User IDs in /api/v4/users/ids

What is CVE-2023-5333?

CVE-2023-5333 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 9 Oct 2023. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Mattermost fails to deduplicate input IDs allowing a simple user to cause the application to consume excessive resources and possibly crash by sending a specially crafted request to /api/v4/users/ids with multiple identical IDs.

Weakness: CWE-400

Which versions are affected by CVE-2023-5333?

1 open source package ship an affected version, including mattermost. It affects 1 product.

Products include Mattermost Mattermost Server.

How do I fix CVE-2023-5333?

Upgrade mattermost to a fixed version for your release line: 7.8.11, 8.0.3 or 8.1.2.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2023-5333 being exploited?

There is no known exploitation of CVE-2023-5333 in the wild and no public exploit code.

Other vulnerabilities in Mattermost Mattermost Server

• CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers Critical 9.9
• CVE-2025-12421 Account Takeover via Code Exchange Endpoint Critical 9.9
• CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User Critical 9.9
• CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards Critical 9.9
• CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive Critical 9.9

All Mattermost Mattermost Server vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-mattermost-2023-5333, GHSA-w28r-7qw2-ghqc.