What’s Vulnerable › Vulnerabilities

CVE-2021-37859: Reflected XSS in OAuth Flow

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 3.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-05 · updated 2026-06-17
• Weakness: CWE-79

Description

Fixed a bypass for a reflected cross-site scripting vulnerability affecting OAuth-enabled instances of Mattermost.

Affected products

• Mattermost App Framework: from 5.32.0 before 5.34.5; from 5.35.0 before 5.35.4; from 5.36.0 before 5.36.1 — fixed in 5.34.5, 5.35.4, 5.36.1

How to fix

Upgrade to a fixed version: Mattermost App Framework 5.34.5, 5.35.4, 5.36.1. Check the vendor advisory for mitigations.

References

• https://mattermost.com/security-updates/
• https://mattermost.com/security-updates/

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