CVE-2017-18906 Mattermost Server vulnerable to user account takeover when Single Sign-On OAuth2 is used
Attackers can claim other users' accounts via OAuth2 SSO flaws, requiring immediate upgrades to Mattermost Server.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2017-18906?
CVE-2017-18906 is a high-severity authentication bypass vulnerability in Mattermost Mattermost Server, published on 19 Jun 2020. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
An issue was discovered in Mattermost Server before 4.0.0, 3.10.2, and 3.9.2, when Single Sign-On OAuth2 is used. An attacker could claim somebody else's account.
Weakness: CWE-287
Which versions are affected by CVE-2017-18906?
5 open source packages ship an affected version, including github.com/mattermost/mattermost-server. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/mattermost/mattermost-server Go | All versions | 3.9.2-0.20170714134023-b17fca0d5ee7 |
github.com/mattermost/mattermost-server Go | All versions | 3.9.2-0.20170714134023-b17fca0d5ee7 |
github.com/mattermost/mattermost-server Go | From 3.10.0 | 3.10.2 |
github.com/mattermost/mattermost-server Go | From 3.10.0 | 3.10.2 |
github.com/mattermost/mattermost-server Go | From 3.10.0+incompatible | 3.10.2+incompatible |
Products include Mattermost Mattermost Server.
How do I fix CVE-2017-18906?
Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 3.9.2-0.20170714134023-b17fca0d5ee7, 3.10.2 or 3.10.2+incompatible.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2017-18906 being exploited?
There is no known exploitation of CVE-2017-18906 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Mattermost Server
- CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers
- CVE-2025-12421 Account Takeover via Code Exchange Endpoint
- CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User
- CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards
- CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive
Sources
Also known as GHSA-fpcr-4rr5-hpcp, GO-2026-4477.