Sudo Command is Vulnerable to Rowhammer. What Else Might Be?

Attacks against Linux were reported to be on the rise in 2022 and  2023; TrendMicro noted a 62% increase in ransomware attacks against Linux systems. Once attackers gain initial access to a Linux system they seek to elevate privileges and establish persistence. To prevent these secondary stages of an attack, the security of Linux systems relies heavily on the effectiveness of tools like the sudo command, which grants users elevated privileges for executing critical commands.

However, recent vulnerabilities, such as CVE-2023-42465, have exposed potential weaknesses in sudo's security architecture, highlighting the need for robust mitigation strategies.

In this article, we explore the significance of the sudo command, delve into the Rowhammer vulnerability, and examine the implications for other software susceptible to similar privilege escalation attacks.

What is the sudo Command?

The sudo command is a Linux and Unix-like operating system tool used for privilege escalation. "Sudo" stands for "superuser do".  When the sudo command is used before any other command in Linux, it allows regular users to execute sensitive commands with elevated privileges, typically reserved for the root user (aka "superuser" or "admin" user in WIndows environments).

By invoking sudo before a command, users can temporarily gain administrative privileges, granting them the ability to perform tasks such as installing malware, modifying system configurations, and accessing files that would otherwise be restricted.

CVE-2023-42465 - Sudo Vulnerable to Privilege Escalation 

CVE-2023-42645, disclosed in [date] is a vulnerability in the Linux sudo command that gives an attacker with local access to a system the ability to escalate their privileges to root. The vulnerability itself does not exploit a traditional software flaw, but rather leverages a side-channel attack known as Rowhammer to change the contents of a memory address.  In the case of CVE-2023-42465 the attacker is attempting to change the contents of the memory register accessed by the sudo command when verifying the user's current privilege level. 

CVE-2023-42645 is described as:

Sudo before 1.9.15 might allow row hammer attacks (for authentication bypass or privilege escalation) because application logic sometimes is based on not equaling an error value (instead of equaling a success value), and because the values do not resist flips of a single bit.

What is the Rowhammer Vulnerability?

The Rowhammer vulnerability is a type of side-channel attack that targets the physical properties of dynamic random-access memory (DRAM) modules. It was first discovered by a group of researchers from Carnegie Mellon University and Intel Labs. Rowhammer exploits a phenomenon where repeated accesses to certain memory rows can cause bit flips in adjacent rows. In other words, by "hammering" on a memory address, attackers can change the contents of a RAM register.

As computer technology has developed, microchips, CPUs and RAM have become increasingly smaller in physical size. The vulnerability occurs due to the leaks in electrical interactions between closely spaced memory cells, causing a disturbance in the charge of neighboring cells. This leakage can lead to unintended changes in memory contents.

Also, several proof-of-concepts and research papers have documented the operational effectiveness of Rowhammer attacks. The research from Google employs memory spraying, utilizing the POSIX-compliant Unix system called mmap() to map files or devices into memory. Through repetitive use of the mmap() system call on a single file, the attacker can saturate a significant portion of physical memory with page tables.

Mitigating Rowhammer Attacks

Since Rowhammer attacks bypass traditional security measures, they are difficult to detect and mitigate. As a result, mitigating Rowhammer vulnerabilities often requires a combination of hardware and software-based solutions, including memory refresh rate adjustments, error-correcting code (ECC) memory, and operating system-level protections.

Here are some state-of-the-art security measures that can be employed to mitigate Rowhammer attacks:

• Generate access controls that follow the principle of least privilege: When designing network security controls it's crucial to protect against privilege escalation attacks using a defense in depth strategy. This includes employing access controls according to the Principle Of Least Privilege (POLP) that limit user permissions to the bare minimum required for their tasks, reducing the potential impact of exploitation by Rowhammer attacks.

• Employ software techniques to refresh memory to a known good state: Several USPTO patents (US20140089576, US20140006703, US20140059287, US20140095780) have been granted that seek to address Rowhammer attacks by refreshing memory contents to a known good state. These patents describe a technology that detects repeated access of a row within a specific time threshold. Known as a "row hammer event," the memory controller detects the event, identifies the affected row, and issues commands to perform targeted refreshes to mitigate the corruption. 

• Employ EDR solutions that can detect and prevent fileless malware attacks: EDR technology is specifically designed to address sophisticated threats like fileless malware that seek to exploit via Rowhammer by monitoring and analyzing endpoint activity in real-time, allowing for early detection and response to malicious activity that traditional security solutions may miss.

• Don't depend on the value of single memory addresses: Relying solely on a single memory address for authentication or authorization checks introduces a single point of failure. Going forward, it is important that software architecture and design should prioritize security against attacks such as Rowhammer by avoiding reliance on a single memory address's value for verifying critical functions. Software functions that verify user permissions for executing privileged system-level commands are at high risk for being exploited by Rowhammer attacks.

What Other Software May Be Vulnerable To Rowhammer Attacks?

Rowhammer attacks can potentially bypass access controls implemented in various software systems. Rowhammer attacks pose a significant threat to software systems that rely on a single bit as a flag to verify authorization, as Rowhammer attacks can selectively flip the value of a single memory address. Consequently, any software employing such simplistic authorization mechanisms is particularly susceptible to exploitation, potentially leading to unauthorized access and compromise of sensitive functionalities or data.

Other software that may be vulnerable to Rowhammer for privilege escalation include:

• Web browsers: Considering that most users access the internet, browser security measures are paramount to enterprise security. Rowhammer can potentially be leveraged via Javascript when a potential victim visits a website to manipulate memory structures, enabling attackers to bypass sandboxing mechanisms or execute arbitrary code in the browser's context. 

• Virtualization software: Rowhammer attacks might compromise the isolation between virtual machines by targeting memory used for virtualization management or hypervisor functions, leading to unauthorized access to sensitive data across virtual environments.

• Other applications: Rowhammer attacks against mapped memory used for other applications such as web administrative portals, VPN servers, database access control, or others could potentially result in unauthorized access to, or modification of, sensitive data stored in databases, undermining data integrity and confidentiality measures.

• Corrupting File Permissions: Rowhammer attacks targeting memory used for managing file permissions could lead to unauthorized access or modification of sensitive files, compromising data integrity and security measures.

• Cryptographic libraries: Rowhammer-induced bit flips in memory regions holding cryptographic keys or intermediate data could compromise the confidentiality and integrity of cryptographic operations, facilitating unauthorized decryption or forging of digital signatures.

Conclusion

In summary, the article highlights the vulnerability of the sudo command to Rowhammer attacks, as evidenced by CVE-2023-42465, which underscores the importance of robust mitigation strategies in Linux systems. Rowhammer attacks exploit physical memory vulnerabilities, posing a significant threat to software systems that rely on simplistic authorization mechanisms.

Beyond sudo, other software such as web browsers, virtualization software, operating system kernels, database servers, and cryptographic libraries may also be susceptible to Rowhammer attacks, necessitating proactive measures to mitigate these risks and protect sensitive data and functionalities.

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