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Description

The following analytic identifies potential exploitation of a previously unknown vulnerability in the Web User Interface (Web UI) feature of Cisco IOS XE software (CVE-2023-20198). Successful exploitation allows an attacker to create an account on the affected device with privilege level 15 access, granting them full control of the compromised device. The detection is based on the observation of suspicious account creation and subsequent actions, including the deployment of an implant consisting of a configuration file. The implant is saved under the file path //usr//binos//conf//nginx-conf//cisco_service.conf and is not persistent, meaning a device reboot will remove it, but the newly created local user accounts remain active even after system reboots. The new user accounts have level 15 privileges, meaning they have full administrator access to the device. This privileged access to the devices and subsequent creation of new users is tracked as CVE-2023-20198.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Web
  • Last Updated: 2023-10-17
  • Author: Michael Haag, Splunk
  • ID: 07c36cda-6567-43c3-bc1a-89dff61e2cd9

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1190 Exploit Public-Facing Application Initial Access
Kill Chain Phase
  • Delivery
NIST
  • DE.CM
CIS20
  • CIS 13
CVE
ID Summary CVSS
CVE-2023-20198 Cisco is providing an update for the ongoing investigation into observed exploitation of the web UI feature in Cisco IOS XE Software. We are updating the list of fixed releases and adding the Software Checker. Our investigation has determined that the actors exploited two previously unknown issues. The attacker first exploited CVE-2023-20198 to gain initial access and issued a privilege 15 command to create a local user and password combination. This allowed the user to log in with normal user access. The attacker then exploited another component of the web UI feature, leveraging the new local user to elevate privilege to root and write the implant to the file system. Cisco has assigned CVE-2023-20273 to this issue. CVE-2023-20198 has been assigned a CVSS Score of 10.0. CVE-2023-20273 has been assigned a CVSS Score of 7.2. Both of these CVEs are being tracked by CSCwh87343. None 


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| tstats count min(_time) as firstTime max(_time) as lastTime from datamodel=Web where Web.url IN ("/webui/logoutconfirm.html?logon_hash=*") Web.http_method=POST Web.status=200 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)`
| `cisco_ios_xe_implant_access_filter`

Macros

The SPL above uses the following Macros:

:information_source: cisco_ios_xe_implant_access_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • Web.http_method
  • Web.url
  • Web.url_length
  • Web.src
  • Web.dest

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, restrict to Cisco IOS XE devices or perimeter appliances. Modify the analytic as needed based on hunting for successful exploitation of CVE-2023-20198.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
81.0 90 90 Possible exploitation of CVE-2023-20198 against $dest$ by $src$.

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

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