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Mattermost Server vulnerable to XSS via an uploaded file

Moderate severity GitHub Reviewed Published May 24, 2022 to the GitHub Advisory Database • Updated Jan 12, 2026

Package

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

Affected versions

< 3.9.2
>= 3.10.0, < 3.10.2

Patched versions

3.9.2
3.10.2

Description

An issue was discovered in Mattermost Server before 4.0.0, 3.10.2, and 3.9.2. It allows XSS via an uploaded file.

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 12, 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.
(58th percentile)

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

CVE ID

CVE-2017-18904

GHSA ID

GHSA-8pff-p3gx-w4jf

Source code

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