CVE-2019-20866 Security feature bypass in n/a
Attackers can bypass IP-based security controls by spoofing the Proxy HTTP header, affecting Mattermost Server deployments.
- 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-2019-20866?
CVE-2019-20866 is a medium-severity 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 5.12.0. Use of a Proxy HTTP header, rather than the source address in an IP packet header, for obtaining IP address information was mishandled.
Weakness: CWE-444
Which versions are affected by CVE-2019-20866?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2019-20866?
No fix has been published for CVE-2019-20866 yet. Limit exposure of the affected software until one is available.
Is CVE-2019-20866 being exploited?
There is no known exploitation of CVE-2019-20866 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-mmmh-x6gq-25cg.