CVE-2018-21256

Name: CVE-2018-21256
Creator: NVD / NIST
Published: 2020-06-19T18:15:10.74+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.3/10EPSS 0.61%

Last modified Jun 17, 2026

CVE-2018-21256 is a medium-severity vulnerability rated 4.3/10 on the CVSS scale. 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.. EPSS estimates a 0.61% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.61%

44.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-732

Affected Software

Vendor	Product	Versions
Mattermost	Mattermost Server	< 5.1.0

References

https://mattermost.com/security-updates/Vendor Advisory
https://mattermost.com/security-updates/Vendor Advisory

Timeline

Published: Jun 19, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2018-21256?

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.

How severe is CVE-2018-21256?

CVE-2018-21256 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.61% probability of exploitation in the next 30 days.

How do I fix CVE-2018-21256?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2018-21256?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST