How severe is GHSA-2v3w-6g35-5f9v?

GHSA-2v3w-6g35-5f9v 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 GHSA-2v3w-6g35-5f9v?

GHSA-2v3w-6g35-5f9v affects the following packages: github.com/mattermost/mattermost/server/v8 (Go), github.com/mattermost/mattermost-server (Go), 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 GHSA-2v3w-6g35-5f9v?

Update github.com/mattermost/mattermost/server/v8 to 8.0.0-20260129181235-1346cf529aef or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-2v3w-6g35-5f9v is resolved across your whole dependency graph.

How do I detect GHSA-2v3w-6g35-5f9v 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 GHSA-2v3w-6g35-5f9v 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 GHSA-2v3w-6g35-5f9v actively exploited in the wild?

No public exploit code has been indexed for GHSA-2v3w-6g35-5f9v 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-2v3w-6g35-5f9v?

GHSA-2v3w-6g35-5f9v has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 23th 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-2v3w-6g35-5f9v?

GHSA-2v3w-6g35-5f9v is classified as CWE-1287 (CWE-1287). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-2v3w-6g35-5f9v published, and has it been updated?

GHSA-2v3w-6g35-5f9v was published on March 16, 2026 and was last updated on March 26, 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 fails to properly validate User-Agent header tokensGHSA-2v3w-6g35-5f9v

MEDIUMFix: mattermost/mattermost@1346cf5

GHSA-2v3w-6g35-5f9v is a medium-severity (CVSS 4.3) CWE-1287 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.

Also known asCVE-2026-25783GO-2026-4725

Published

Mar 16, 2026

Updated

Mar 26, 2026

Affected

5 pkgs

Patched

5 / 5

Exploits

None indexed

Exploitation data as of Nov 6, 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-2v3w-6g35-5f9v.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk+0.01%

Lower risk than most CVEs23th percentile — riskier than 23% 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

5 pkgs affected

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

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586

Affected Packages

5 total 5 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost/server/v8`	all versions	8.0.0-20260129181235-1346cf529aef`go get github.com/mattermost/mattermost/server/v8@v8.0.0-20260129181235-1346cf529aef`
🐹Go	`github.com/mattermost/mattermost-server`	all versions	5.3.2-0.20260129181235-1346cf529aef`go get github.com/mattermost/mattermost-server@v5.3.2-0.20260129181235-1346cf529aef`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 10.11.0-rc1&&< 10.11.11	10.11.11`go get github.com/mattermost/mattermost-server@v10.11.11`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 11.2.0-rc1&&< 11.2.3	11.2.3`go get github.com/mattermost/mattermost-server@v11.2.3`
🐹Go	`github.com/mattermost/mattermost-server`	≥ 11.3.0-rc1&&< 11.3.1	11.3.1`go get github.com/mattermost/mattermost-server@v11.3.1`

Affected Products

1 product · 3 configurations

Application

mattermost servermattermost

≥ 11.3.0 && < 11.3.1

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/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 8.0.0-20260129181235-1346cf529aef or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-2v3w-6g35-5f9v 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 GHSA-2v3w-6g35-5f9v 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-1287CWE-1287

Weaponization

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

Timeline

Disclosed

Mar 16, 2026

Last updated

Mar 26, 2026

Identifiers

GHSA-2v3w-6g35-5f9v

GO-2026-4725

References

Advisorynvd.nist.gov · CVE 2026 25783 Webgithub.com · 1346cf529aef0672c39a56ec10d1b8a9c8fb387d Webmattermost.com · security updates Packagegithub.com · mattermost

Related vulnerabilities

This CVE is medium severity; 7 of 8 other CVEs affecting v8 are rated as high or higher (top: high).

CVE-2026-8823CVE-2026-6046CVE-2026-7387CVE-2026-6961CVE-2026-7184CVE-2026-6689CVE-2026-6739CVE-2026-3433

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedMar 26, 2026

Mattermost fails to properly validate User-Agent header tokensGHSA-2v3w-6g35-5f9v

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 GHSA-2v3w-6g35-5f9v in your dependencies?