Overview
A recently discovered vulnerability, designated as CVE-2025-5689, poses a significant threat to systems using the pre-auth Network Security Services (NSS). This flaw could potentially lead to a full system compromise or data leakage, making it a high-risk issue demanding immediate attention. This vulnerability affects all users logging in for the first time on target systems, inadvertently granting them root group access. This vulnerability matters because it can provide a malicious actor with high-level privileges, leading to unauthorized access, data manipulation, or even system control.
Vulnerability Summary
CVE ID: CVE-2025-5689
Severity: Critical (CVSS 8.5)
Attack Vector: Network
Privileges Required: Low
User Interaction: Required
Impact: Potential system compromise and data leakage
Affected Products
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Product | Affected Versions
Pre-Auth NSS | All Versions
How the Exploit Works
The flaw is rooted in the temporary user record that the authd uses in the pre-auth NSS. When a user logs in for the first time, the system erroneously assigns them to the root group for the duration of that SSH session. A malicious user could exploit this flaw to gain root access to the system, leading to unauthorized actions such as data modification, system control, or data exfiltration.
Conceptual Example Code
Imagine a scenario where an attacker has established an SSH session using a new user account. The vulnerability would allow the attacker to execute commands with root privileges due to the incorrect group assignment. The pseudo-code below demonstrates this:
# The attacker logs in via SSH
ssh newuser@target.example.com
# The system incorrectly assigns the new user to the root group
groups
root
# The attacker now executes a command with root privileges
sudo cat /etc/shadowIn this example, the ‘cat /etc/shadow’ command would typically be inaccessible to a new user. However, due to the CVE-2025-5689 vulnerability, the attacker has root access and can view sensitive system files, leading to a potential system compromise.
Mitigation and Prevention
The recommended course of action to mitigate this vulnerability is to apply the vendor-provided patch as soon as it becomes available. Until then, a temporary mitigation can be implemented by using a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) to monitor SSH sessions and identify any suspicious activity. Additionally, system administrators should consider limiting the number of new users or restricting their access until the patch is applied.