How severe is GHSA-r5vf-grcx-5vqp?

GHSA-r5vf-grcx-5vqp has a CVSS score of 5.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by GHSA-r5vf-grcx-5vqp?

GHSA-r5vf-grcx-5vqp affects the following packages: github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-plugin-github (Go). Ecosystems affected: Go.

How do I fix GHSA-r5vf-grcx-5vqp?

Update github.com/mattermost/mattermost-server to 11.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-r5vf-grcx-5vqp is resolved across your whole dependency graph.

How do I detect GHSA-r5vf-grcx-5vqp 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-r5vf-grcx-5vqp 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 GHSA-r5vf-grcx-5vqp actively exploited in the wild?

No public exploit code has been indexed for GHSA-r5vf-grcx-5vqp 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-r5vf-grcx-5vqp?

GHSA-r5vf-grcx-5vqp has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 13th 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-r5vf-grcx-5vqp?

GHSA-r5vf-grcx-5vqp 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 GHSA-r5vf-grcx-5vqp published, and has it been updated?

GHSA-r5vf-grcx-5vqp was published on May 26, 2026 and was last updated on July 7, 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

Mattermost allows authenticated users to gain access to private repositoriesGHSA-r5vf-grcx-5vqp

MEDIUMFix: mattermost/mattermost-plugin-github@6e6b740

GHSA-r5vf-grcx-5vqp is a medium-severity (CVSS 5.4) CWE-863 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-2026-28735GO-2026-5839

Published

May 26, 2026

Updated

Jul 7, 2026

Affected

5 pkgs

Patched

5 / 5

Exploits

None indexed

Exploitation data as of Oct 7, 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 GHSA-r5vf-grcx-5vqp.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs13th percentile — riskier than 13% of all scored CVEsHighest risk

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

How urgent is this, really

GHSA-r5vf-grcx-5vqp by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 384,189 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

5 pkgs affected

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

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 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628

Affected Packages

5 total 5 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost-server`	≥ 11.6.0&&< 11.6.1	11.6.1`go get github.com/mattermost/mattermost-server@v11.6.1`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 11.5.0&&< 11.5.4	11.5.4`go get github.com/mattermost/mattermost-server@v11.5.4`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 11.4.0&&< 11.4.5	11.4.5`go get github.com/mattermost/mattermost-server@v11.4.5`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 10.11.0&&< 10.11.15	10.11.15`go get github.com/mattermost/mattermost-server@v10.11.15`
🐹Go	`github.com/mattermost/mattermost-plugin-github`	all versions	1.0.1-0.20260318132218-6e6b740c4852`go get github.com/mattermost/mattermost-plugin-github@v1.0.1-0.20260318132218-6e6b740c4852`

Affected Products

1 product · 4 configurations

Application

mattermost servermattermost

≥ 11.6.0 && < 11.6.1

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 11.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-r5vf-grcx-5vqp 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 GHSA-r5vf-grcx-5vqp in your dependencies?

Find it across Go, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

5.4/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

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

CWE Classification

CWE-863CWE-863

Weaponization

No known public exploit tooling found.

Timeline

Disclosed

May 26, 2026

Last updated

Jul 7, 2026

Identifiers

GHSA-r5vf-grcx-5vqp

GO-2026-5839

References

Advisorynvd.nist.gov Webgithub.com Webmattermost.com Packagegithub.com

Related vulnerabilities

This CVE is medium severity; 7 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-2026-6046CVE-2026-7387CVE-2026-6961

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 7, 2026