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Grey Box Penetration Testing

Definition: Grey Box Testing is a software testing methodology that combines elements of both black box and white box testing approaches. It involves having partial knowledge of the internal workings of an application, typically limited to high-level diagrams or documentation, while testing from the external perspective like a user.

What is Grey Box Penetration Testing?

Grey box penetration testing gets its name from blending both white and black box testing. The tester is granted some internal knowledge of the assets under review. It is particularly useful for security professionals or penetration testers as it simulates an attack by someone who has some insider knowledge but still operates from outside the security perimeter. It helps in identifying vulnerabilities that might not be visible through black box testing alone and does not require the level of detail needed for white box testing.

By offering a balance between the two extremes, grey box security testing can provide more comprehensive coverage of an application’s security profile, making it an effective means of identifying both surface-level and deep-seated vulnerabilities. Grey box testing is often much more cost-effective and efficient than a black box, as the tester saves a considerable amount of time from having to discover information about the targets.

Grey Box PenetrationTesting methodology

The methodologies deployed by grey box testing aim to strike some balance between black and white box testing, hence grey. Grey box security testing will typically require some limited knowledge of the assets’s internal workings. Like both Black and White box testing, the grey box also follows a sequence of steps. Each step is designed to explore and identify vulnerabilities. The more information the assessor has, the easier it will be to exploit specific vulnerabilities.

  • Intelligence Gathering: With limited knowledge of the environment, the intelligence gathering phase of grey box testing aims to use the already known information (which could be configuration information, architecture diagrams, API documentation) as a basis to gather even information about the systems. Tools such as Nmap could be used (with a defined list of assets given by a client) to understand the available services more deeply.
  • Vulnerability Analysis: Using the information from the previous phase, a tester can then make educated guesses about potential security issues. This could include utilising existing tools (such as BurpSuite or Nessus) to further interact with the services, examining the security of specific assets, and documenting the results.
  • Exploitation: Now the tester is armed with all of the knowledge from the previous two phases. The tester will try and exploit the identified issues. This could involve utilising custom or semi-custom exploits that are tailored to the specific assets within the scope. Tools such as Metasploit, or the exploit database could be used at this phase.
  • Post-Exploitation: If the tester has now gained some access, the goal is to understand the extent of the actions they can perform on the assets. This could include data exfiltration, moving laterally through the network or even escalating the privileges so that the tester can perform even more actions.
  • Analysis and Reporting: Once all the results have been compiled into carefully written notes. The tester will perform a thorough analysis of the results, ruling out false positives. The tester will then usually write a technical report, providing recommendations (If applicable) and a risk analysis of the discovered issues.

Grey Box Security Testing Examples

Let’s go through some examples of Grey Box Testing using real-world examples, and probable outcomes:

AWS Configuration Review

A company has recently migrated to an AWS environment and wants to ensure that the new environment is secure. A penetration tester is provided with access to the environment and limited information about what services may be accessible. The tester uses sophisticated tools such as Prowler, CloudMapper, and Scoutsuite to enumerate the AWS configuration in search of security misconfigurations.

Outcome: The grey box security test uncovers publicly accessible storage buckets containing sensitive information and overly permissive roles that allow escalation of privileges.

Mobile Application Security Audit

A financial services company wants to ensure that its new, online-only mobile backing application is secure, before launching it on the app store. The penetration tester is provided with the application binaries and backend API documentation. The tester performs both dynamic and static analysis of the binaries intending to detect issues with the system, such as insecure data storage, improper session management, or specific vulnerabilities with the backend APIs.

Outcome: The tester identifies some sensitive information, such as PINs and account numbers, are stored insecurely on the device. They also discovered that session tokens are not properly invalidated after logout. The findings lead to a significant improvement in the security posture of the application.

Network Penetration Testing for a Corporate Network

A corporate network with multiple subnets and services undergoes a penetration test. The pen tester is given multiple network diagrams, no user credentials are given, and a list of network assets to target. They are tasked with identifying any security misconfigurations that could be exploited by an internal attacker.

Outcome: The tester discovers the use of LLMNR and NBT-NS on the network, the use of these legacy protocols (for the most part), allows the attacker to poison SMB requests and obtain hashed credentials. The tester cracks the credentials using Hashcat and uses these credentials to stage further attacks on the network.

The above examples serve as a guide for how penetration testing can be conducted from a grey-box perspective. Each of the examples shows how grey box testing can be used to perform successful penetration testing.

Key Characteristics:

  • Partial Knowledge: Testers have some knowledge of the software’s internal structures but not complete access to the source code.
  • Combines Approaches: Utilises techniques from both black box and white box testing.
  • Efficiency: Often quicker and less resource-intensive than pure white box testing.
  • Greater Coverage: Can uncover a broader range of issues by considering the application’s internal and external operations.

Related Terms:

  • Black Box Penetration Testing: Testing the functional aspects of software by only interacting with the external interfaces and having no knowledge of the internal workings.
  • White Box Penetration Testing: In-depth testing based on full knowledge of the application’s source code, pathways, and infrastructure.
  • Ethical Hacking: The practice of legally breaking into computers and devices to test an organisation’s defences, often using grey box testing methods.

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