How severe is CVE-2016-11063?

CVE-2016-11063 has a CVSS score of 6.1/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2016-11063?

CVE-2016-11063 affects the following packages: github.com/mattermost/mattermost-server (Go). Ecosystems affected: Go.

How do I fix CVE-2016-11063?

Update github.com/mattermost/mattermost-server to 3.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-11063 is resolved across your whole dependency graph.

How do I detect CVE-2016-11063 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 CVE-2016-11063 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 CVE-2016-11063 actively exploited in the wild?

No public exploit code has been indexed for CVE-2016-11063 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 CVE-2016-11063?

CVE-2016-11063 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 52th 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 CVE-2016-11063?

CVE-2016-11063 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 CVE-2016-11063 published, and has it been updated?

CVE-2016-11063 was published on June 19, 2020 and was last updated on July 31, 2026. 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

MEDIUM severity

CVE-2016-11063 — mattermost-server

MEDIUMFix: mattermost/mattermost@48533aa

CVE-2016-11063 is a medium-severity (CVSS 6.1) 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.

Mattermost Server vulnerable to Cross-site Scripting through file preview feature

Also known asGHSA-cffj-7w5c-jqjhGO-2025-4045

Published

Jun 19, 2020

Updated

Jul 31, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 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 CVEs52th percentile — riskier than 52% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹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 3.5.1. XSS can occur via file preview.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost-server`	all versions	3.5.1`go get github.com/mattermost/mattermost-server@v3.5.1`

Affected Products

1 product · 1 configurations

Application

mattermost servermattermost

< 3.5.1

range

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 3.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-11063 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 3.5.1. XSS can occur via file preview.

O3 Security · Impact-Aware SCA

Is CVE-2016-11063 in your dependencies?

Find it across Go, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

6.1/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE Classification

CWE-79Cross-site Scripting (XSS)

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

OpenSSF Scorecard

Package health score

mattermost

7.3/10

Dependency-Update-Tool10/10

Maintained10/10

Code-Review10/10

Branch-Protection4/10

Vulnerabilities0/10

Assessed Oct 22, 2026

Timeline

Disclosed

Jun 19, 2020

Last updated

Jul 31, 2026

Identifiers

CVE-2016-11063

GHSA-cffj-7w5c-jqjh

GO-2025-4045

References

Advisorymattermost.com · security updates Advisorynvd.nist.gov · CVE 2016 11063 Webgithub.com · 48533aa483879a19fdd2c1e09c596aa6c028d439 Webgithub.com · mattermost Webmattermost.com · security updates

Related vulnerabilities

This CVE is medium severity; 6 of 8 other CVEs affecting mattermost-server are rated as high or higher (top: high).

CVE-2026-5139CVE-2026-8074CVE-2026-9162CVE-2026-6673CVE-2026-6062CVE-2026-8823CVE-2026-6046CVE-2026-7387

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 31, 2026