CVE-2018-21257 Missing authorization in n/a
Attackers can bypass access restrictions to modify channel headers via the slash command API in Mattermost Server.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2018-21257?
CVE-2018-21257 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 19 Jun 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for setting a channel header) via the Channel header slash command API.
Weakness: CWE-862
Which versions are affected by CVE-2018-21257?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2018-21257?
No fix has been published for CVE-2018-21257 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2018-21257 being exploited?
There is no known exploitation of CVE-2018-21257 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-qg8w-6226-7h2q.