Unrestricted Telnet Access in Azure NSGs

ID: azure-nsg-telnet-unrestricted

Severity: high

Author: princechaddha

Tags: cloud,devops,azure,microsoft,nsg,azure-cloud-config

Description

Ensure that Microsoft Azure network security groups (NSGs) do not allow unrestricted access on TCP port 23, used by Telnet, to prevent unauthorized command execution.

YAML Source

id: azure-nsg-telnet-unrestricted
info:
  name: Unrestricted Telnet Access in Azure NSGs
  author: princechaddha
  severity: high
  description: |
    Ensure that Microsoft Azure network security groups (NSGs) do not allow unrestricted access on TCP port 23, used by Telnet, to prevent unauthorized command execution.
  impact: |
    Unrestricted Telnet access can lead to unauthorized command execution, allowing attackers to gain control over network resources.
  remediation: |
    Modify NSG rules to restrict access on TCP port 23. Only allow access from secure, authenticated sources and consider using more secure alternatives like SSH.
  reference:
    - https://docs.microsoft.com/en-us/azure/virtual-network/network-security-groups-overview
  tags: cloud,devops,azure,microsoft,nsg,azure-cloud-config

flow: |
  code(1);
  for (let NsgData of iterate(template.nsgdata)) {
    NsgData = JSON.parse(NsgData)
    set("nsg", NsgData.name)
    set("resourcegroup", NsgData.resourceGroup)
    code(2)
  }

self-contained: true
code:
  - engine:
      - sh
      - bash
    source: |
      az network nsg list --query '[*].{name:name, resourceGroup:resourceGroup}' --output json

    extractors:
      - type: json
        name: nsgdata
        internal: true
        json:
          - '.[]'

  - engine:
      - sh
      - bash
    source: |
      az network nsg rule list --nsg-name $nsg --resource-group $resourcegroup --query "[?direction=='Inbound' && access=='Allow' && protocol=='TCP' && (destinationPortRange=='23')]"

    matchers:
      - type: word
        words:
          - '"sourceAddressPrefix": "*"'
          - '"sourceAddressPrefix": "internet"'
          - '"sourceAddressPrefix": "any"'

    extractors:
      - type: dsl
        dsl:
          - 'nsg + " has unrestricted access on TCP port 23"'
# digest: 490a0046304402203ee06d83ef3e9a13b3e5f05f5b6f6e6f7ee88e4b354b23aba69995693d8ff89d02203a37f4cb28d4c529bab7466548b181750acb685e91704759ccb8925157e1e23f:922c64590222798bb761d5b6d8e72950

Guide to check the vulnerabilities

This template is used to detect vulnerabilities in web applications. It can be used with the Nuclei tool to scan for specific patterns or behaviors.

$ nuclei -u "URL" -t "cloud/azure/network/azure-nsg-telnet-unrestricted.yaml"

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