How severe is CVE-2017-18894?

CVE-2017-18894 has a CVSS score of 8.1/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2017-18894?

CVE-2017-18894 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 CVE-2017-18894?

Update github.com/mattermost/mattermost-server to 4.0.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-18894 is resolved across your whole dependency graph.

How do I detect CVE-2017-18894 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-2017-18894 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2017-18894 actively exploited in the wild?

No public exploit code has been indexed for CVE-2017-18894 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-2017-18894?

CVE-2017-18894 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 58th 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-2017-18894?

CVE-2017-18894 is classified as CWE-732 (CWE-732). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2017-18894 published, and has it been updated?

CVE-2017-18894 was published on June 19, 2020 and was last updated on October 24, 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

HIGH severity

CVE-2017-18894 — mattermost-server

HIGH

CVE-2017-18894 is a high-severity (CVSS 8.1) CWE-732 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 has intermittent Authorization bypass for resource-owners

Also known asGHSA-gg42-mwr6-p82cGO-2026-4297

Published

Jun 19, 2020

Updated

Oct 24, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs58th percentile — riskier than 58% 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

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 4.2.0, 4.1.1, and 4.0.5, when used as an OAuth 2.0 service provider. Resource-owner authorization can be intermittently bypassed, allowing account takeover.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost-server`	all versions	4.0.5`go get github.com/mattermost/mattermost-server@v4.0.5`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 4.1.0&&< 4.1.1	4.1.1`go get github.com/mattermost/mattermost-server@v4.1.1`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 4.2.0-rc1&&< 4.2.0	4.2.0`go get github.com/mattermost/mattermost-server@v4.2.0`

Affected Products

1 product · 6 configurations

Application

mattermost servermattermost

≥ 4.1.0 && < 4.1.1

1 version

4.2.0

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 4.0.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-18894 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2017-18894 in your dependencies?

Find it across Go, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

8.1/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Raw vector

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

CWE Classification

CWE-732CWE-732

Weaponization

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

OpenSSF Scorecard

Package health score

mattermost

7.3/10

Maintained10/10

Dependency-Update-Tool10/10

Code-Review10/10

Branch-Protection4/10

Vulnerabilities0/10

Assessed Nov 8, 2026

Timeline

Disclosed

Jun 19, 2020

Last updated

Oct 24, 2026

Identifiers

CVE-2017-18894

GHSA-gg42-mwr6-p82c

GO-2026-4297

References

Advisorymattermost.com · security updates Advisorynvd.nist.gov · CVE 2017 18894 Webmattermost.com · security updates Packagegithub.com · mattermost

Related vulnerabilities

This CVE is high severity; 1 of 8 other CVEs affecting mattermost-server is 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 verifiedOct 24, 2026