How severe is CVE-2026-6343?

CVE-2026-6343 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-2026-6343?

CVE-2026-6343 affects the following packages: github.com/mattermost/mattermost/server/v8 (Go), github.com/mattermost/mattermost/server/v8 (Go), github.com/mattermost/mattermost/server/v8 (Go), github.com/mattermost/mattermost-plugin-playbooks (Go). Ecosystems affected: Go.

How do I fix CVE-2026-6343?

Update github.com/mattermost/mattermost/server/v8 to 11.5.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6343 is resolved across your whole dependency graph.

How do I detect CVE-2026-6343 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/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-6343 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-6343 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-6343 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-2026-6343?

CVE-2026-6343 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 17th 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-2026-6343?

CVE-2026-6343 is classified as CWE-863 (CWE-863). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-6343 published, and has it been updated?

CVE-2026-6343 was published on May 18, 2026 and was last updated on August 12, 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-2026-6343 — v8

MEDIUMFix: mattermost/mattermost-plugin-playbooks@887d9ca

CVE-2026-6343 is a medium-severity (CVSS 4.3) CWE-863 vulnerability in github.com/mattermost/mattermost/server/v8. A fix is available for github.com/mattermost/mattermost/server/v8 — see the affected versions and patch details below.

Mattermost Playbooks Plugin fails to enforce view permissions in list endpoints, allowing unauthorized access to public playbooks

Also known asGHSA-m79q-8qf5-v622GO-2026-5494

Published

May 18, 2026

Updated

Aug 12, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Sep 29, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-6343.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs17th percentile — riskier than 17% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2026-6343 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 380,526 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

4 pkgs affected

🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost-plugin-playbooks

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

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to check public/private permissions which allows members without these permissions to access public playbooks via /get.. Mattermost Advisory ID: MMSA-2026-00591

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost/server/v8`	≥ 11.5.0&&< 11.5.2	11.5.2`go get github.com/mattermost/mattermost/server/v8@v11.5.2`
🐹Go	`github.com/mattermost/mattermost/server/v8`	≥ 11.4.0&&< 11.4.4	11.4.4`go get github.com/mattermost/mattermost/server/v8@v11.4.4`
🐹Go	`github.com/mattermost/mattermost/server/v8`	≥ 10.11.0&&< 10.11.14	10.11.14`go get github.com/mattermost/mattermost/server/v8@v10.11.14`
🐹Go	`github.com/mattermost/mattermost-plugin-playbooks`	all versions	1.41.1-0.20260309184833-887d9cacb616`go get github.com/mattermost/mattermost-plugin-playbooks@v1.41.1-0.20260309184833-887d9cacb616`

Affected Products

1 product · 3 configurations

Application

mattermost servermattermost

≥ 11.5.0 && < 11.5.2

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/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/mattermost/mattermost/server/v8 to 11.5.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6343 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2026-6343 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

Low

Integrity

None

Availability

None

Raw vector

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

CWE Classification

CWE-863CWE-863

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

mattermost-plugin-playbooks

7.2/10

Code-Review10/10

Maintained10/10

Branch-Protection5/10

Assessed Sep 28, 2026

Timeline

Disclosed

May 18, 2026

Last updated

Aug 12, 2026

Identifiers

CVE-2026-6343

GHSA-m79q-8qf5-v622

GO-2026-5494

References

Advisorygithub.com Advisorymattermost.com Advisorynvd.nist.gov Webgithub.com Packagegithub.com

Related vulnerabilities

This CVE is medium severity; 8 of 8 other CVEs affecting v8 are rated as high or higher (top: high).

CVE-2026-6046CVE-2026-7387CVE-2026-6961CVE-2026-7184CVE-2026-6689CVE-2026-6739CVE-2026-3433CVE-2026-4915

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedAug 12, 2026

CVE-2026-6343 — v8

Exploitation Status

No confirmed exploitation observed yet

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-2026-6343 in your dependencies?