What is a Memory Corruption Vulnerability?

If your IT infrastructure relies on Linux distributions, you likely experienced difficulties when the PwnKit memory corruption vulnerability was disclosed in January 2022. The CVE-2021-4034 PwnKit vulnerability affected Linux distributions worldwide, including Red Hat and SuSE. Despite decades of memory exploit mitigation by major OS providers like Microsoft, this recent disclosure demonstrates that memory corruption exploits will persist, leaving no one immune.

This article aims to explain what a memory corruption vulnerability is, how it makes IT operations vulnerable to attacks, and how you can defend against such attacks. Let's get started.

To grasp memory corruption, we need to understand how memory is used in modern applications. As applications grow more complex with a large code base, developers must adhere to programming best practices to manage memory efficiently. 

However, unintentional memory corruption issues, such as buffer overflows and dangling pointers, can occur when developers allocate memory incorrectly. 

Let's briefly explore these scenarios and how they arise.

Memory corruption happens when a system's memory is altered without a specific assignment, causing changes to the contents of that memory location due to programming errors. 

Inefficient memory management can lead to inadvertent use of allocated memory, corrupting memory blocks and providing an opportunity for malicious actors to exploit. Now, let's describe two significant scenarios:

Memory overflow

The most common exploit is memory overflow, which occurs when code allows users to input more information than the allocated memory block can hold. This overflow can overwrite data blocks or execute malicious code by providing addresses outside the allocated space.

Dangling pointers

A pointer is a data structure that stores a memory address, referencing a location in the memory to obtain the stored value. A dangling pointer arises when the pointer points to previously freed memory or fails to point to a valid object. 

This creates security vulnerabilities such as information leaks or privilege escalations. Another scenario involves a failure to reset the pointer effectively, potentially pointing to memory assigned to a different application. Vulnerabilities introduced in such scenarios are known as 'Use After Free' or UAF vulnerabilities.

Memory corruption issues are frequently reported, prompting OS providers like Microsoft and Linux distributions such as SuSE and RedHat to implement measures that make memory corruption more difficult to exploit. They employ memory thresholds and timing constraints. However, thoroughly implementing these safety checks in complex environments with frequent updates remains challenging.

These vulnerabilities can lead to various exploits by attackers, including:

• Accessing sensitive data with code insertions

• Executing code with elevated privileges

• System crashes or denials of service

Since OS installations are customized for specific customer needs, memory corruption vulnerabilities can go undetected for months, giving attackers a head start before security research teams become aware of them.

So, how can you thwart attackers and prevent exploits? The following tips will help you prepare your IT teams to mitigate and stay ahead of these attacks.

Even if your IT team is aware of an existing memory corruption vulnerability, manually deploying patches and reconfigurations to each endpoint can become a logistical nightmare. To plan effectively, follow this checklist for your mitigation strategy:

1. Prepare an endpoint inventory

Maintain a complete inventory of endpoints, categorized by OS version and flavor, especially for Linux distributions. This inventory will allow you to isolate specific endpoints in the future if you know the impacted OS or application.

2. Deploy strong security controls

Preventing memory corruption exploits can be incredibly challenging, but implementing stringent access policies, permissions, and advanced authentication controls like Multi-Factor Authentication (MFA) can enhance your security by enforcing "trust, but verify" principles.

3. Enforce good development and testing standards

Regularly use robust memory debugging tools to check your applications and OS customizations. This practice helps detect and remediate issues until a formal OS patch is available.

4. Execute an action plan for affected endpoints

If a fix is identified, promptly execute an action plan to patch the impacted endpoints. While it may not be feasible to fix all affected endpoints immediately, consider your team's options to eventually remove the affected software from a given set of server resources. Alternatively, isolate the server by taking it offline if necessary. Automating these actions across your endpoints can expedite the process and ensure no endpoint is overlooked.