CVE-2026-40016 — Attacker can upload a malicious Sieve script over

title: CVE-2026-40016 - Malicious Sieve Script Upload via ManageSieve
id: scw-2026-05-12-ai-1
status: experimental
level: medium
description: |
  Detects the upload of a Sieve script via the ManageSieve service that attempts to bypass CPU limits. This rule specifically looks for POST requests to a '/manage-sieve' endpoint containing '.sieve' in the query and a script payload indicative of attempting to execute commands or bypass limits, which is characteristic of CVE-2026-40016.
author: SCW Feed Engine (AI-generated)
date: 2026-05-12
references:
  - https://shimiscyberworld.com/posts/nvd-CVE-2026-40016/
tags:
  - attack.persistence
  - attack.t1505.003
logsource:
    category: webserver
detection:
  selection:
      cs-uri|contains:
          - '/manage-sieve'
      cs-method|contains:
          - 'POST'
      sc-status|startswith:
          - '2'
      cs-uri-query|contains:
          - '.sieve'
  selection_script_content:
      TargetFilename|contains:
          - 'require [ "vnd.dovecot.execute"]
          - 'vnd.dovecot.execute "/bin/bash -c "'
      condition: selection AND selection_script_content
falsepositives:
  - Legitimate administrative activity

Source: Shimi's Cyber World · License & reuse