CVE-2023-40703 Denial of Service via specially crafted block fields in Mattermost Boards

What is CVE-2023-40703?

CVE-2023-40703 is a medium-severity denial of service vulnerability in Mattermost Mattermost, published on 27 Nov 2023. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Mattermost fails to properly limit the characters allowed in different fields of a block in Mattermost Boards allowing a attacker to consume excessive resources, possibly leading to Denial of Service, by patching the field of a block using a specially crafted string.

Weakness: CWE-400

Which versions are affected by CVE-2023-40703?

8 open source packages ship an affected version, including github.com/mattermost/mattermost/server/v8 and github.com/mattermost/mattermost-server/v6. It affects 1 product.

Products include Mattermost Mattermost.

How do I fix CVE-2023-40703?

Upgrade github.com/mattermost/mattermost/server/v8 to a fixed version for your release line: 8.1.4, 9.0.2 or 9.1.1.

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-2023-40703 being exploited?

There is no known exploitation of CVE-2023-40703 in the wild and no public exploit code.

Other vulnerabilities in Mattermost Mattermost

• CVE-2019-20851 Path traversal in n/a Critical 9.1
• CVE-2024-39274 Malicious remote can add users to arbitrary teams and channels High 8.7
• CVE-2024-39777 Malicious remote can invite itself to an arbitrary local channel High 8.7
• CVE-2024-39830 Timing attack during remote cluster token comparison when shared channels are enabled High 8.1
• CVE-2023-3615 Lack of server certificate validation in websockets connection High 8.1

All Mattermost Mattermost vulnerabilities

Sources

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

Also known as GHSA-c37r-v8jx-7cv2.