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Mattermost Server does not neutralize HTML content in an Email template field

Moderate severity GitHub Reviewed Published May 24, 2022 to the GitHub Advisory Database • Updated Jan 14, 2026

Package

gomod github.com/mattermost/mattermost-server (Go)

Affected versions

< 4.0.5
>= 4.1.0, < 4.1.1
>= 4.2.0-rc1, < 4.2.0

Patched versions

4.0.5
4.1.1
4.2.0

Description

An issue was discovered in Mattermost Server before 4.2.0, 4.1.1, and 4.0.5. E-mail templates can have a field in which HTML content is not neutralized.

References

Published by the National Vulnerability Database Jun 19, 2020
Published to the GitHub Advisory Database May 24, 2022
Reviewed Jan 12, 2026
Last updated Jan 14, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(47th percentile)

Weaknesses

Improper Encoding or Escaping of Output

The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved. Learn more on MITRE.

CVE ID

CVE-2017-18892

GHSA ID

GHSA-wj5w-qghh-gvqp

Source code

Credits

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