CVE-2018-21259 Denial of service in n/a
Attackers can cause a denial of service by sending a malformed link in a channel, hanging the application.
- 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-2018-21259?
CVE-2018-21259 is a medium-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 4.10.1, 4.9.4, and 4.8.2. It allows attackers to cause a denial of service (application hang) via a malformed link in a channel.
Weakness: CWE-20
Which versions are affected by CVE-2018-21259?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2018-21259?
No fix has been published for CVE-2018-21259 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-2018-21259 being exploited?
There is no known exploitation of CVE-2018-21259 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-w5xj-4h4h-82v2.