CVE-2025-9078 Weak cache keys lead to post IDOR and link preview poisoning

What is CVE-2025-9078?

CVE-2025-9078 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 15 Sep 2025. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Mattermost versions 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 9.11.x <= 9.11.17, 10.10.x <= 10.10.1, 10.9.x <= 10.9.3 fail to properly validate cache keys for link metadata which allows authenticated users to access unauthorized posts and poison link previews via hash collision attacks on FNV-1 hashing

Weakness: CWE-328

Which versions are affected by CVE-2025-9078?

16 open source packages ship an affected version, including github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server/v5 and github.com/mattermost/mattermost-server/v6. It affects 1 product.

Products include Mattermost Mattermost Server.

How do I fix CVE-2025-9078?

Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 10.10.2, 10.5.9, 10.8.4 or 10.9.4.

Is CVE-2025-9078 being exploited?

There is no known exploitation of CVE-2025-9078 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 GHSA-9p92-x77w-9fw2, GO-2025-3959.