CVE-2019-20857 Denial of service in n/a
Attackers can cause a denial of service in Mattermost Server by sending input with many backtick characters, hanging the markdown renderer.
- 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-2019-20857?
CVE-2019-20857 is a high-severity denial of service 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 5.16.0. It allows attackers to cause a denial of service (markdown renderer hang) via many backtick characters.
Which versions are affected by CVE-2019-20857?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2019-20857?
No fix has been published for CVE-2019-20857 yet. Limit exposure of the affected software until one is available.
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-2019-20857 being exploited?
There is no known exploitation of CVE-2019-20857 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-957g-g8r7-fp94.