CVE-2023-27320: Sudo Double-Free Vulnerability in Per-Command Chroot Feature Before Version 1.9.13p2

The world of cybersecurity is constantly evolving, and staying up to date with the latest vulnerabilities and exploits is extremely important for any systems administrator, security researcher, or IT enthusiast. Today, we will discuss a recently discovered vulnerability in the popular Linux utility, Sudo. Designated as CVE-2023-27320, this vulnerability involves a double-free issue that affects Sudo before version 1.9.13p2's per-command chroot feature. In this post, we will fully explain the vulnerability, its exploit details, provide code snippets showcasing the issue, and reference original sources for more information.

Understanding the Vulnerability: Double-Free Issue
To comprehend this vulnerability, let's first grasp the concept of a double-free issue. A double-free occurs when a programming bug causes a region of memory to be freed or deallocated twice. When this occurs, it can result in a wide range of problems, such as application crashes, undefined behavior, and, most critically, potential security hazards that could be leveraged by an attacker to execute arbitrary code on the target system.

How the Double-Free Affects Sudo Per-Command Chroot Feature
The vulnerability, CVE-2023-27320, affects Sudo's per-command chroot feature, which allows users to execute a command within a chroot environment, without the need to operate the chroot command first. In Sudo versions before 1.9.13p2, a double-free error in this feature can potentially be exploited by an attacker, granting them unauthorized access to the target system.

Code Snippet Showcasing the Issue
To better understand the vulnerability, let's examine a code snippet that demonstrates the double-free issue in Sudo's per-command chroot feature. The code presented below is an example and not taken directly from Sudo source code.

#include <stdlib.h>

int main(void) {
    char *buffer = (char *) malloc(100);  // Allocate memory for the buffer.
    
    some_function(buffer);  // Execute a function, which could trigger the vulnerability.

    free(buffer);  // Deallocate the memory for the buffer.
    buffer = NULL; // Set buffer pointer to NULL
   
    ... // Additional code

    if (buffer != NULL) {
        free(buffer);  // This line causes a double-free if the memory was already freed earlier.
    }
}

void some_function(char *buf) {
    ... // More code

    if (error_condition) {  
        free(buf);  // Memory is freed here upon an error condition.
        buf = NULL; // Set buf pointer to NULL
        return;
    }
}

In the code snippet above, the double-free issue arises when the some_function function deallocates the memory with a free() function call upon encountering an error condition. Later on, the memory is freed once more in the main() function, causing the double-free error.

Exploit Details and Attack Scenarios
An attacker could potentially exploit the double-free vulnerability in Sudo's per-command chroot feature by crafting specially designed Sudo configuration files or command-line arguments. By exploiting this vulnerability, the attacker could gain unauthorized access to the target system, execute arbitrary code with root privileges, and ultimately compromise the security of the system.

To defend against this attack, it is vital to update Sudo to version 1.9.13p2 or later, thereby eliminating the double-free vulnerability.

References and Original Sources
For more in-depth information about CVE-2023-27320 and the double-free vulnerability in Sudo before version 1.9.13p2, please refer to these original sources:

1. The CVE entry for CVE-2023-27320 hosted on the MITRE Corporation's CVE website.
2. The Sudo homepage offering details on Sudo, along with the latest patch and version details.
3. The Sudo 1.9.13p2 release announcement describing changes and the fix for the discussed vulnerability.

Conclusion
In this long-read post, we examined the double-free vulnerability in the per-command chroot feature of Sudo before version 1.9.13p2, designated as CVE-2023-27320. By understanding the vulnerability, reviewing code snippets that showcase the issue, and examining exploit details, you can effectively address this vulnerability to secure your systems. Updating to the current version of Sudo is highly recommended as a mitigation means against potential exploitation.

Timeline

Published on: 02/28/2023 18:15:00 UTC
Last modified on: 04/13/2023 17:15:00 UTC