CVE-2017-18078 : Security Advisory and Response

In versions of systemd prior to 237, a vulnerability exists in systemd-tmpfiles that allows unauthorized local users to bypass access restrictions by exploiting hard links to files they do not have write access to, potentially leading to privilege escalation.

Understanding CVE-2017-18078

What is CVE-2017-18078?

CVE-2017-18078 is a vulnerability in systemd-tmpfiles in systemd versions before 237 that enables unauthorized local users to alter ownership and permissions of files through hard links, circumventing access restrictions.

The Impact of CVE-2017-18078

The vulnerability allows local users to escalate privileges by manipulating ownership of critical system files, such as /etc/passwd, leading to unauthorized access and potential system compromise.

Technical Details of CVE-2017-18078

Vulnerability Description

systemd-tmpfiles in systemd versions prior to 237 supports ownership/permission changes on hardlinked files, even when fs.protected_hardlinks sysctl is disabled.
Unauthorized local users can exploit this behavior by creating hard links to files they lack write access to, like altering ownership of /etc/passwd.

Affected Systems and Versions

Product: N/A
Vendor: N/A
Versions affected: N/A

Exploitation Mechanism

Local users create hard links to files they do not have write access to, such as critical system files.

Mitigation and Prevention

Immediate Steps to Take

Update systemd to version 237 or newer to mitigate the vulnerability.
Monitor system logs for any unauthorized ownership or permission changes.

Long-Term Security Practices

Implement the principle of least privilege to restrict user access.
Regularly review and update system configurations to enhance security.

Patching and Updates

Apply patches and updates provided by the system vendor to address the vulnerability.