CVE-2019-20859 Auth bypass in n/a
Attackers can bypass login access controls in Mattermost Server via crafted input, potentially gaining unauthorized access to user accounts.
- 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-2019-20859?
CVE-2019-20859 is a high-severity authentication bypass 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 5.15.0. Login access control can be bypassed via crafted input.
Which versions are affected by CVE-2019-20859?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2019-20859?
No fix has been published for CVE-2019-20859 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2019-20859 being exploited?
There is no known exploitation of CVE-2019-20859 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-4gmh-fvqj-9v7g.