# CVE-2025-13821: server — Fix Available

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

# CVE-2025-13821 — server

MEDIUM [Fix: mattermost/mattermost@cd17b61](https://github.com/mattermost/mattermost/commit/cd17b61de41bf0a49b524bb91ce0bbe859e5a100)

CVE-2025-13821 is a medium-severity (CVSS 5.7) Information Exposure 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.

User profile update exposes password hash and MFA secrets

Also known as[GHSA-pp9j-pf5c-659x](/vulnerability/GHSA-pp9j-pf5c-659x)GO-2026-4524

Published

Feb 16, 2026

Updated

Nov 7, 2026

Affected

5 pkgs

Patched

2 / 5

Exploits

None indexed

Exploitation data as of Nov 2, 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-2025-13821.

## EPSS Exploitation Probability

[via FIRST.org ↗](https://www.first.org/epss/)

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs15th percentile — riskier than 15% of all scored CVEsHighest risk

0.00%0.25%0.49%0.74%0.0%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.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 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to sanitize sensitive data in WebSocket messages which allows authenticated users to exfiltrate password hashes and MFA secrets via profile nickname updates or email verification events. Mattermost Advisory ID: MMSA-2025-00560

## Affected Packages

5 total 2 fixed

Ecosystem

Package

Vulnerable range

Fix

🐹Go

`github.com/mattermost/mattermost/server/v8` 

all versions

8.0.0-20251210191531-cd17b61de41b`go get github.com/mattermost/mattermost/server/v8@v8.0.0-20251210191531-cd17b61de41b`

🐹Go

`github.com/mattermost/mattermost-server` 

≥ 11.1.0

No fix

🐹Go

`github.com/mattermost/mattermost-server` 

≥ 10.11.0

No fix

🐹Go

`github.com/mattermost/mattermost-server` 

≥ 11.2.0

No fix

🐹Go

`github.com/mattermost/mattermost-server` 

all versions

5.3.2-0.20251210191531-cd17b61de41b`go get github.com/mattermost/mattermost-server@v5.3.2-0.20251210191531-cd17b61de41b`

## Affected Products

1 product · 3 configurations

Application

`mattermost server`mattermost

≥ 11.2.0 && < 11.2.2

range

## Detection & mitigation playbook

Open-source dependency

1.  ### 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.
    
2.  ### Fix
    
    Update github.com/mattermost/mattermost/server/v8 to 8.0.0-20251210191531-cd17b61de41b or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-13821 is resolved across your whole dependency graph.
    
3.  ### Workarounds
    
    Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.
    

## Frequently Asked Questions

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to sanitize sensitive data in WebSocket messages which allows authenticated users to exfiltrate password hashes and MFA secrets via profile nickname updates or email verification events. Mattermost Advisory ID: MMSA-2025-00560

O3 Security · Impact-Aware SCA

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