How severe is GHSA-9x8x-w6g5-hx4w?

No CVSS score has been assigned to GHSA-9x8x-w6g5-hx4w yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-9x8x-w6g5-hx4w?

GHSA-9x8x-w6g5-hx4w affects the following packages: github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server (Go). Ecosystems affected: Go.

How do I fix GHSA-9x8x-w6g5-hx4w?

Update github.com/mattermost/mattermost-server to 4.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9x8x-w6g5-hx4w is resolved across your whole dependency graph.

How do I detect GHSA-9x8x-w6g5-hx4w in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-9x8x-w6g5-hx4w if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is GHSA-9x8x-w6g5-hx4w actively exploited in the wild?

No public exploit code has been indexed for GHSA-9x8x-w6g5-hx4w yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-9x8x-w6g5-hx4w?

GHSA-9x8x-w6g5-hx4w has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 53th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-9x8x-w6g5-hx4w?

GHSA-9x8x-w6g5-hx4w is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was GHSA-9x8x-w6g5-hx4w published, and has it been updated?

GHSA-9x8x-w6g5-hx4w was published on May 24, 2022 and was last updated on December 9, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

Mattermost Server is vulnerable to XSS attacks against an OAuth 2.0 allow/deny pageGHSA-9x8x-w6g5-hx4w

GHSA-9x8x-w6g5-hx4w is a Cross-site Scripting (XSS) vulnerability in github.com/mattermost/mattermost-server. A fix is available for github.com/mattermost/mattermost-server — see the affected versions and patch details below.

Also known asCVE-2017-18877GO-2025-4190

Published

May 24, 2022

Updated

Dec 9, 2025

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs53th percentile — riskier than 53% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

3 pkgs affected

🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. XSS attacks could occur against an OAuth 2.0 allow/deny page.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost-server`	all versions	4.1.2`go get github.com/mattermost/mattermost-server@v4.1.2`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 4.2.0&&< 4.2.1	4.2.1`go get github.com/mattermost/mattermost-server@v4.2.1`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 4.3.0-rc1&&< 4.3.0	4.3.0`go get github.com/mattermost/mattermost-server@v4.3.0`

Affected Products

1 product · 6 configurations

Application

mattermost servermattermost

≥ 4.2.0 && < 4.2.1

1 version

4.3.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/mattermost/mattermost-server to 4.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9x8x-w6g5-hx4w is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. XSS attacks could occur against an OAuth 2.0 allow/deny page.

O3 Security · Impact-Aware SCA

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