How severe is CVE-2017-18878?

CVE-2017-18878 has a CVSS score of 4.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2017-18878?

CVE-2017-18878 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-2017-18878?

Update github.com/mattermost/mattermost-server to 4.1.2-0.20171004201910-6be8113eb60c or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-18878 is resolved across your whole dependency graph.

How do I detect CVE-2017-18878 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-2017-18878 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-2017-18878 actively exploited in the wild?

No public exploit code has been indexed for CVE-2017-18878 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-2017-18878?

CVE-2017-18878 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 56th 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-2017-18878?

CVE-2017-18878 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-2017-18878 published, and has it been updated?

CVE-2017-18878 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

MEDIUM severity

CVE-2017-18878 — mattermost-server

MEDIUMFix: mattermost/mattermost@6be8113

CVE-2017-18878 is a medium-severity (CVSS 4.3) 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 allows users with a session ID to revoke another users' session

Also known asGHSA-h564-6gc2-fcc6GO-2025-4191

Published

Jun 19, 2020

Updated

Oct 24, 2026

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 ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs56th percentile — riskier than 56% 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 4.3.0, 4.2.1, and 4.1.2. Knowledge of a session ID allows revoking another user's session.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost-server`	all versions	4.1.2-0.20171004201910-6be8113eb60c`go get github.com/mattermost/mattermost-server@v4.1.2-0.20171004201910-6be8113eb60c`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 4.2.0-rc1&&< 4.2.1-0.20171004192657-8fbbd688ea24	4.2.1-0.20171004192657-8fbbd688ea24`go get github.com/mattermost/mattermost-server@v4.2.1-0.20171004192657-8fbbd688ea24`
🐹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 4.1.2-0.20171004201910-6be8113eb60c or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-18878 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

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. Knowledge of a session ID allows revoking another user's session.

O3 Security · Impact-Aware SCA

Is CVE-2017-18878 in your dependencies?

Find it across Go, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

4.3/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Raw vector

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

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

Code-Review10/10

Dependency-Update-Tool10/10

Vulnerabilities0/10

Branch-Protection4/10

Assessed Nov 4, 2026

Timeline

Disclosed

Jun 19, 2020

Last updated

Oct 24, 2026

Identifiers

CVE-2017-18878

GHSA-h564-6gc2-fcc6

GO-2025-4191

References

Advisorymattermost.com · security updates Advisorynvd.nist.gov · CVE 2017 18878 Webgithub.com · 6be8113eb60cf5ddd2dc1c3f4db05cae0c183086 Webgithub.com · 8fbbd688ea2466dd0d70e9c07e9703d78f8a19a5 Webgithub.com · affd35071ea155069979fd359726296de8aa6aaf Webmattermost.com · security updates Packagegithub.com · mattermost

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 verifiedOct 24, 2026

CVE-2017-18878 — mattermost-server

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2017-18878 in your dependencies?