Windows Exchange Autodiscover SSRF Abuse

name: Windows Exchange Autodiscover SSRF Abuse
id: d436f9e7-0ee7-4a47-864b-6dea2c4e2752
version: 8
date: '2026-03-10'
author: Michael Haag, Nathaniel Stearns, Splunk
status: production
type: TTP
description: This analytic identifies potential exploitation attempts of ProxyShell (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207) and ProxyNotShell (CVE-2022-41040, CVE-2022-41082) vulnerabilities in Microsoft Exchange Server. The detection focuses on identifying the SSRF attack patterns used in these exploit chains. The analytic monitors for suspicious POST requests to /autodiscover/autodiscover.json endpoints that may indicate attempts to enumerate LegacyDN attributes as part of initial reconnaissance. It also detects requests containing X-Rps-CAT parameters that could indicate attempts to impersonate Exchange users and access the PowerShell backend. Additionally, it looks for MAPI requests that may be used to obtain user SIDs, along with suspicious user agents (particularly Python-based) commonly used in automated exploit attempts. If successful, these attacks can lead to remote code execution as SYSTEM, allowing attackers to deploy webshells, access mailboxes, or gain persistent access to the Exchange server and potentially the broader network environment.
data_source:
    - Windows IIS
search: |-
    | tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Web
      WHERE (
            Web.status=200
        )
        AND Web.http_method=POST
      BY Web.src Web.status Web.uri_path
         Web.dest Web.http_method Web.uri_query
         Web.http_user_agent
    | `drop_dm_object_name("Web")`
    | eval is_autodiscover=if(like(lower(uri_path),"%autodiscover/autodiscover.json%"),1,0)
    | eval has_rps_cat=if(like(lower(uri_query),"%x-rps-cat=%"),1,0)
    | eval exchange_backend=if(like(lower(uri_query),"%/powershell/?%"),1,0)
    | eval mapi=if(like(uri_query,"%/mapi/%"),1,0)
    | eval suspicious_agent=if(match(lower(http_user_agent), "python
    | urllib"),1,0)
    | addtotals fieldname=Score is_autodiscover, has_rps_cat, exchange_backend, mapi, suspicious_agent
    | where Score >= 3
    | fields Score, src, dest, status, uri_query, uri_path, http_method, http_user_agent
    | `windows_exchange_autodiscover_ssrf_abuse_filter`
how_to_implement: To successfully implement this search you need to be ingesting information on Web traffic, Exchange OR IIS logs, mapped to `Web` datamodel in the `Web` node. In addition, confirm the latest CIM App 4.20 or higher is installed.
known_false_positives: False positives are limited.
references:
    - https://www.gteltsc.vn/blog/warning-new-attack-campaign-utilized-a-new-0day-rce-vulnerability-on-microsoft-exchange-server-12715.html
    - https://msrc-blog.microsoft.com/2022/09/29/customer-guidance-for-reported-zero-day-vulnerabilities-in-microsoft-exchange-server/
    - https://twitter.com/GossiTheDog/status/1575762721353916417?s=20&t=67gq9xCWuyPm1VEm8ydfyA
    - https://twitter.com/cglyer/status/1575793769814728705?s=20&t=67gq9xCWuyPm1VEm8ydfyA
    - https://www.gteltsc.vn/blog/warning-new-attack-campaign-utilized-a-new-0day-rce-vulnerability-on-microsoft-exchange-server-12715.html
    - https://research.splunk.com/stories/proxyshell/
    - https://splunk.github.io/splunk-add-on-for-microsoft-iis/
    - https://highon.coffee/blog/ssrf-cheat-sheet/
    - https://owasp.org/Top10/A10_2021-Server-Side_Request_Forgery_%28SSRF%29/
    - https://m365internals.com/2022/10/18/hunting-and-responding-to-proxyshell-attacks/
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") starthoursago=168  | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: Activity related to ProxyShell or ProxyNotShell has been identified on $dest$. Review events and take action accordingly.
    risk_objects:
        - field: dest
          type: system
          score: 50
    threat_objects: []
tags:
    analytic_story:
        - ProxyShell
        - BlackByte Ransomware
        - ProxyNotShell
        - Seashell Blizzard
    asset_type: Web Server
    cve:
        - CVE-2021-34523
        - CVE-2021-34473
        - CVE-2021-31207
        - CVE-2022-41040
        - CVE-2022-41082
    mitre_attack_id:
        - T1190
        - T1133
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: network
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1190/proxyshell/proxyshell.log
          source: ms:iis:splunk
          sourcetype: ms:iis:splunk