CVE-2018-21256
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended...
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
NVD Score used
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.
- Record
CVE-2018-21256- CVSS 3.1
- 4.3 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N - CVSS 2.0
- 4.0 Medium
AV:N/AC:L/Au:S/C:N/I:P/A:N - Weakness
- CWE-732
- Updated
- 2026-11-02
CVE List No score
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.
- Record
CVE-2018-21256- Updated
- 2026-11-02
EUVDEUVD-2018-13771 No score
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.
- Record
EUVD-2018-13771- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-7fjj-c6hx-jhxv No score
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended...
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.
- Record
GHSA-7fjj-c6hx-jhxv- Updated
- 2026-11-02
OSV
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.
- Record
CVE-2018-21256- CVSS 3.1
- 4.3 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-02
Affected products
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2018-21256 is a medium vulnerability (CVSS 4.3) in Mattermost Server, published June 19, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.61%, the 49th percentile. No source names a fixed version.