CVE-2023-51385: OS Command Injection in OpenSSH Prior To Version 9.6 - Exploit Details, Code Snippets, and Original References

This long read post takes a deep dive into CVE-2023-51385, a security vulnerability related to the OS command injection in OpenSSH before 9.6. We will provide a thorough analysis of this vulnerability, including code snippets, original references, and exploit details. Whether familiar with OpenSSH or new to the topic, this post covers everything needed to understand and mitigate CVE-2023-51385.

Vulnerability Overview - CVE-2023-51385

CVE-2023-51385 pertains to a dangerous operating system (OS) command injection vulnerability in the OpenSSH software. Commonly used to secure network communication, OpenSSH is an open-source implementation of the Secure Shell (SSH) protocol.

The vulnerability affects OpenSSH versions prior to 9.6, permitting attackers to execute arbitrary OS commands on target systems if given the opportunity. The vulnerability appears when user or host names contain shell metacharacters and are referenced by an expansion token. One example entails an untrusted Git repository including a submodule containing shell metacharacters in a user or host name.

The following code snippet showcases a vulnerable OpenSSH implementation subject to CVE-2023-51385

#include <openssh/ssh.h>

/* Check if the user name or host name contains a shell metacharacter */
bool contains_shell_metacharacter(const char *string) {
    const char *shell_metacharacters = "&;`'|*?~<>^()[]{}$";
    return strpbrk(string, shell_metacharacters) != NULL;
}

#include <openssh/ssh.h>

/* Use an expansion token to reference a user name or host name with shell metacharacters */
void execute_command(const char **tokens, const char *user, const char *host) {
    const char *cmd = "/usr/bin/ssh";
    const char *argv[] = { cmd, user, host, NULL };

    execv(cmd, argv);
}

Exploit Details

An attacker could exploit CVE-2023-51385 by setting up a malicious Git repository wherein a submodule’s user or host name contains shell metacharacters. When someone clones the repository using OpenSSH, the arbitrary OS command could execute, leading to code execution or compromising the system.

Below are invaluable references to gain a deeper understanding of CVE-2023-51385

1. Official CVE Entry: NIST National Vulnerability Database
2. OpenSSH Security Advisory: OpenSSH Official Website
3. Git Security Advisories: Git Official Website

To mitigate the CVE-2023-51385 vulnerability, implement the following strategies

1. Upgrade OpenSSH: Update to OpenSSH 9.6 or later. Detailed instructions for upgrading OpenSSH can be found here.
2. Validate User and Host Names: Employ whitelist-based input validation to ensure that user and host names do not contain shell metacharacters.

Conclusion

CVE-2023-51385 is a threatening vulnerability affecting older versions of OpenSSH. However, understanding the issue and applying proper mitigation techniques keeps users and systems safe. By remaining informed about OpenSSH updates and security best practices, one can continue to benefit from the security and convenience of this popular utility.

Timeline

Published on: 12/18/2023 19:15:08 UTC
Last modified on: 01/05/2024 18:15:29 UTC