CVE-2023-4966 Exploitation Attempt - Citrix ADC Sensitive Information Disclosure - Webserver

Status: test
Severity: high
Log source: category webserver
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects exploitation attempt of CVE-2023-4966 a Citrix ADC and NetScaler Gateway sensitive information disclosure vulnerability via webserver logs by looking for a very long host header string.

Known false positives

Vulnerability scanners

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application

Rule body

title: CVE-2023-4966 Exploitation Attempt - Citrix ADC Sensitive Information Disclosure - Webserver
id: a4e068b5-e27c-4f21-85b3-e69e5a4f7ce1
related:
    - id: 87c83d8e-5390-44ce-aa4a-d3b37e54d0a0 # Webserver Attempt
      type: similar
    - id: ff349b81-617f-4af4-924f-dbe8ea9bab41 # Proxy Attempt
      type: similar
    - id: aee7681f-b53d-4594-a9de-ac51e6ad3362 # Proxy Exploit
      type: similar
status: test
description: Detects exploitation attempt of CVE-2023-4966 a Citrix ADC and NetScaler Gateway sensitive information disclosure vulnerability via webserver logs by looking for a very long host header string.
references:
    - https://support.citrix.com/article/CTX579459/netscaler-adc-and-netscaler-gateway-security-bulletin-for-cve20234966-and-cve20234967
    - https://attackerkb.com/topics/2faW2CxJgQ/cve-2023-4966
    - https://www.rapid7.com/blog/post/2023/10/25/etr-cve-2023-4966-exploitation-of-citrix-netscaler-information-disclosure-vulnerability/
    - https://www.assetnote.io/resources/research/citrix-bleed-leaking-session-tokens-with-cve-2023-4966
    - https://github.com/assetnote/exploits/tree/main/citrix/CVE-2023-4966
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-11-28
tags:
    - attack.initial-access
    - attack.t1190
    - cve.2023-4966
    - detection.emerging-threats
logsource:
    category: webserver
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem|contains: '/oauth/idp/.well-known/openid-configuration'
        cs-host|re: '.{150}'
    condition: selection
falsepositives:
    - Vulnerability scanners
level: high

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    cs-method: 'GET'
    cs-uri-stem|contains: '/oauth/idp/.well-known/openid-configuration'
    cs-host|re: '.{150}'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`cs-host`	regex_match	`.{150}`	`field:"cs-host" kind:regex_match value:".{150}"`
`cs-method`	eq	`GET`	`field:"cs-method" kind:eq value:"GET"`
`cs-uri-stem`	match	`/oauth/idp/.well-known/openid-configuration`	`field:"cs-uri-stem" kind:match value:"/oauth/idp/.well-known/openid-configuration"`