---
id: "CVE-2026-19621"
kind: "vulnerability"
aliases: ["CVE-2026-19621"]
title: "Mattermost: channel members can read integration webhook secrets from posts"
severity: "medium"
cvss: 6.5
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["chat", "mattermost", "runtime", "self-hosted", "webhooks"]
not_affected_if: ["no-interactive-message-integrations", "unpatched-versions-only"]
published_at: "2026-10-16T08:17:13+00:00"
first_seen_at: "2026-10-23T21:57:12+00:00"
updated_at: "2026-10-25T03:57:58+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-19621", "first_seen_at": "2026-10-23T21:57:12+00:00"}]
---

# Mattermost: channel members can read integration webhook secrets from posts

Mattermost fails to strip action integration secrets from post payloads sent over the post_deleted websocket event and the threads REST API. An authenticated channel member can read server-side webhook URLs and authentication context from interactive-message posts.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the running Mattermost version with `mattermost version` or the System Console version display
- Compare against affected ranges: 11.10.x up to `11.10.0`, 11.9.x up to `11.9.1`, 11.8.x up to `11.8.5`, 11.7.x up to `11.7.9`

## Fix

- Upgrade Mattermost to a release that includes the fix from advisory MMSA-2026-00766 (fixed version unknown from the sources)
- Rotate any webhook URLs or integration tokens used by interactive-message actions if exposure is suspected

## Timeline

- 2026-10-23T21:57:12+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-19621

## From the sources

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to strip action integration secrets from post payloads before broadcasting post-deletion web socket events and returning thread API responses, which allows an authenticated channel member to obtain server-side webhook URLs and authentication context from interactive-message posts via the post_deleted websocket event or the threads REST API.. Mattermost Advisory ID: MMSA-2026-00766

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_