Reflected XSS in OAuth Flow
Priority LOW 37CWE-79Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- Required
- Attack complexity
- High
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- High · High · Low
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-79.
Summary
Fixed a bypass for a reflected cross-site scripting vulnerability affecting OAuth-enabled instances of Mattermost.
Why it matters now
EPSS 0.03288 88th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 5.34.5, 5.35.4
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Mattermost | Mattermost | 5.32.0 – 5.36.0 | 5.34.5, 5.35.4 | Patch available | CNA |
- Mattermost VendorMattermost Affected 5.32.0 – 5.36.0 Fixed in 5.34.5, 5.35.4 Patch available CNA
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost:*:*:*:*:*:*:*:* | 5.32.0 to before 5.34.5; 5.35.0 to before 5.35.4; 5.36.0 to before 5.36.1 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost:*:*:*:*:*:*:*:* Versions 5.32.0 to before 5.34.5; 5.35.0 to before 5.35.4; 5.36.0 to before 5.36.1 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 5.34.5, 5.35.4
Timeline
- 2026-10-02 Threatist record created from CVE-2021-37859
- 2026-10-03 Alias added: GHSA-r4f6-w245-8wv4
References
Advisory 1
More Mattermost vulnerabilities
- TI-2024-26695 Malicious remote can invite itself to an arbitrary local channel CVSS 3.1CRITICAL 9.6
- TI-2023-02056 Oauth authorization codes do not expire when deauthorizing an oauth2 app CVSS 3.1CRITICAL 9.1
- TI-2019-15069 An issue was discovered in Mattermost Mobile Apps before 1.26.0. CVSS 3.1CRITICAL 9.1
- TI-2024-26233 Malicious remote can add users to arbitrary teams and channels CVSS 3.1HIGH 8.7
- TI-2024-26746 Permanently local data deletion by malicious remote CVSS 3.1HIGH 8.7
- TI-2023-06508 Injection in Mattermost CVSS 3.1HIGH 8.8
Sources
- CVE-2021-37859 · CVE Program
- CVE-2021-37859 · NVD
- FIRST EPSS
- GHSA-r4f6-w245-8wv4 · GitHub Advisory Database · CC BY 4.0
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