CVE-2026-42887 — Cross-Site Scripting (XSS)

title: CVE-2026-42887 - Audiobookshelf Login Page XSS via Custom Message
id: scw-2026-05-11-ai-1
status: experimental
level: high
description: |
  Detects the specific stored XSS vulnerability in Audiobookshelf's login page. An attacker with administrative privileges can exploit the `authLoginCustomMessage` field in the `/api/auth-settings` endpoint to inject malicious HTML/JavaScript. This rule looks for POST requests to `/api/auth-settings` containing the vulnerable parameter with common XSS payloads, indicating an attempt to inject script into the login page.
author: SCW Feed Engine (AI-generated)
date: 2026-05-11
references:
  - https://shimiscyberworld.com/posts/nvd-CVE-2026-42887/
tags:
  - attack.initial_access
  - attack.t1189
logsource:
    category: webserver
detection:
  selection:
      cs-uri|endswith:
          - '/api/auth-settings'
      cs-method|exact:
          - 'POST'
      cs-uri-query|contains:
          - 'authLoginCustomMessage'
      sc-status|exact:
          - '200'
  selection_indicators:
      cs-uri-query|contains:
          - '<script>'
          - 'alert('
          - 'onerror='
      condition: selection AND selection_indicators
falsepositives:
  - Legitimate administrative activity

Source: Shimi's Cyber World · License & reuse