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detections/web/citrix_adc_exploitation_cve_2023_3519.yml

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+name: Citrix ADC Exploitation CVE-2023-3519
+id: 76ac2dcb-333c-4a77-8ae9-2720cfae47a8
+version: 1
+date: '2023-07-21'
+author: Michael Haag, Splunk
+status: production
+type: Hunting
+data_source: []
+description: This analytic is designed to assist in hunting for potential exploitation attempts against Citrix ADC in relation to CVE-2023-3519. This vulnerability, identified within Citrix ADC and NetScaler Gateway, appears to be linked with SAML processing components, with an overflow issue allowing for possible memory corruption. Preliminary findings indicate that for the exploit to be viable, SAML has to be enabled. The analytic targets POST requests to certain web endpoints which have been associated with the exploitation process. \
+
+  Given the specific nature of the vulnerability, upon deploying this analytic it is recommended to filter and narrow the focus towards your ADC assets to reduce potential noise and improve the signal of the analytic. Please note that the exploitation of this vulnerability has been reported in the wild, therefore monitoring for potential signs of exploitation should be considered high priority. \
+
+  The search query provided examines web data for POST requests made to specific URLs associated with the exploitation of this vulnerability. It aggregates and presents data to highlight potential exploitation attempts, taking into account elements like user agent, HTTP method, URL length, source, and destination. \
+
+  Please be aware that this analytic is based on current understanding of the vulnerability, and adjustments may be required as more information becomes available.
+search: '| tstats count min(_time) as firstTime max(_time)
+  as lastTime from datamodel=Web where Web.url IN ("*/saml/login","/cgi/samlauth","*/saml/activelogin","/cgi/samlart?samlart=*","*/cgi/logout")  Web.http_method=POST 
+  by Web.http_user_agent, Web.status Web.http_method, Web.url, Web.url_length, Web.src, Web.dest, sourcetype
+  | `drop_dm_object_name("Web")`
+  | `security_content_ctime(firstTime)` 
+  | `security_content_ctime(lastTime)` | `citrix_adc_exploitation_cve_2023_3519_filter`'
+how_to_implement: This detection requires the Web datamodel to be populated from a
+  supported Technology Add-On like Splunk for Apache, Splunk for Nginx, or Splunk
+  for Palo Alto.
+known_false_positives: False positives may be present based on organization use of SAML utilities. Filter, or restrict the analytic to Citrix devices only.
+references:
+- https://blog.assetnote.io/2023/07/21/citrix-CVE-2023-3519-analysis/
+- https://support.citrix.com/article/CTX561482/citrix-adc-and-citrix-gateway-security-bulletin-for-cve20233519-cve20233466-cve20233467
+tags:
+  analytic_story:
+  - Citrix Netscaler ADC CVE-2023-3519
+  cve:
+  - CVE-2023-3519
+  asset_type: Network
+  atomic_guid: []
+  confidence: 50
+  impact: 90
+  message: Possible expliotation of CVE-2023-3519 against $dest$. 
+  mitre_attack_id:
+  - T1190
+  observable:
+  - name: dest
+    type: Hostname
+    role:
+    - Victim
+  product:
+  - Splunk Enterprise
+  - Splunk Enterprise Security
+  - Splunk Cloud
+  risk_score: 45
+  required_fields:
+  - _time
+  - Web.http_method
+  - Web.url
+  - Web.url_length
+  - Web.src
+  - Web.dest
+  security_domain: endpoint
+tests:
+- name: True Positive Test
+  attack_data:
+  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1190/citrix/citrix-cve20233519.log
+    source: pan:threat
+    sourcetype: pan:threat

stories/citrix_netscaler_adc_cve_2023_3519.yml

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+name: Citrix Netscaler ADC CVE-2023-3519
+id: 094df1fe-4345-4c01-8a0f-c65cf7b758bd
+version: 1
+date: '2023-07-20'
+author: Michael Haag, Splunk
+description: The CVE-2023-3519 vulnerability in NetScaler (formerly Citrix) Application Delivery Controller (ADC) and NetScaler Gateway has been exploited by threat actors, as detailed in a recent advisory. The unauthenticated remote code execution vulnerability was utilized as a zero-day to establish a webshell on a non-production environment NetScaler ADC appliance within a critical infrastructure organization. This facilitated the execution of discovery on the victim's active directory and the collection and exfiltration of data. The advisory offers a comprehensive examination of the threat actors' tactics, techniques, and procedures (TTPs), alongside recommended detection methods and incident response guidelines. Immediate patch application from Citrix and the use of the detection guidance in the advisory is strongly recommended for critical infrastructure organizations to mitigate system compromises.
+narrative: Recent advisories have highlighted the exploitation of CVE-2023-3519, a critical vulnerability in Citrix's NetScaler Application Delivery Controller (ADC) and NetScaler Gateway. In June 2023, threat actors utilized this vulnerability to implant a webshell on a NetScaler ADC appliance within a critical infrastructure organization's non-production environment. This action granted them the ability to perform active directory discovery, data collection, and exfiltration. Notably, attempts for lateral movement to a domain controller were obstructed by network-segmentation controls. \
+
+  The compromised organization reported the breach, leading Citrix to issue a patch on July 18, 2023. Multiple advisories have since outlined the threat actors' tactics, techniques, and procedures (TTPs), including their initial access, persistence, privilege escalation, defense evasion, credential access, discovery, collection, command and control, and impact. These advisories also provide detection methods and recommend incident response measures. \
+
+  The threat actors executed several activities during their attack, such as uploading a TGZ file with a generic webshell, discovery script, and setuid binary on the ADC appliance; conducting SMB scanning on the subnet; using the webshell for active directory enumeration and data exfiltration; and accessing NetScaler configuration files and decryption keys. They also decrypted an active directory credential, queried the active directory for various information, encrypted collected data, exfiltrated it as an image file, and attempted to erase their artifacts. Despite these actions, further discovery and lateral movement were impeded due to the organization's network-segmentation controls. \ 
+
+  Advisories suggest conducting specific checks on the ADC shell interface to detect signs of compromise. If a compromise is detected, organizations should isolate potentially affected hosts, reimage compromised hosts, provide new account credentials, collect and review artifacts, and report the compromise. To mitigate the threat, organizations are advised to promptly install the relevant updates for NetScaler ADC and NetScaler Gateway, adhere to cybersecurity best practices, and apply robust network-segmentation controls on NetScaler appliances and other internet-facing devices. \
+references:
+  - https://attackerkb.com/topics/si09VNJhHh/cve-2023-3519
+  - https://www.cisa.gov/sites/default/files/2023-07/aa23-201a_csa_threat_actors_exploiting_citrix-cve-2023-3519_to_implant_webshells.pdf
+  - https://support.citrix.com/article/CTX561482/citrix-adc-and-citrix-gateway-security-bulletin-for-cve20233519-cve20233466-cve20233467
+tags:
+  analytic_story: Citrix Netscaler ADC CVE-2023-3519
+  category:
+  - Adversary Tactics
+  product:
+  - Splunk Enterprise
+  - Splunk Enterprise Security
+  - Splunk Cloud
+  usecase: Advanced Threat Detection