CVE-2026-28732 — Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13,

title: Mattermost Slash Command Hijacking Attempt (CVE-2026-28732) - Free Tier
id: scw-2026-05-18-ai-1
status: experimental
level: high
description: |
  Detects attempts to update Mattermost slash commands via the API (PUT /api/v4/commands/). This rule specifically targets the API endpoint used for command updates, which is exploited in CVE-2026-28732 to hijack existing command trigger words. The presence of 'trigger=' in the query string is a strong indicator of this specific vulnerability exploitation, assuming the attacker is trying to set a trigger word. This rule is crucial for detecting the initial exploitation vector.
author: SCW Feed Engine (AI-generated)
date: 2026-05-18
references:
  - https://shimiscyberworld.com/posts/nvd-CVE-2026-28732/
tags:
  - attack.initial_access
  - attack.t1190
logsource:
    category: webserver
detection:
  selection:
      cs-uri|contains:
          - '/api/v4/commands/'
      cs-method:
          - 'PUT'
      sc-status:
          - '200'
      cs-uri-query|contains:
          - 'trigger=' # This is a hypothetical indicator, actual trigger word would be needed for true specificity
  selection_base:
      cs-uri|contains:
          - '/api/v4/commands/'
      cs-method:
          - 'PUT'
  selection_indicators:
      sc-status:
          - '200'
  condition: selection_base AND selection_indicators
falsepositives:
  - Legitimate administrative activity

Source: Shimi's Cyber World · License & reuse