Overview
CVE-2025-39665 describes a user enumeration vulnerability found in NagVis’ Checkmk MultisiteAuth. This vulnerability affects versions prior to 1.9.48. An unauthenticated attacker can exploit this flaw to enumerate valid Checkmk usernames. This information can then potentially be used in further attacks, such as brute-force attempts or social engineering.
Technical Details
The vulnerability resides within the authentication handling of the Checkmk MultisiteAuth component in NagVis. The specific mechanism allowing user enumeration is not fully detailed in the publicly available descriptions, but the vulnerability has been addressed in NagVis version 1.9.48. The fix likely involves changes to how the system handles invalid authentication attempts, preventing the leakage of information that can be used to determine valid usernames. Analysis of the commit details can give further insights.
Looking at the resolved commit, it seems the vulnerability was plugged by altering the response to failed login attempts. Prior to the fix, the response differed slightly based on whether the username existed, which allowed enumeration. The fix normalizes the response, masking the existence of the username.
CVSS Analysis
Currently, a CVSS score is not available for CVE-2025-39665 (N/A). While user enumeration vulnerabilities are often considered low severity on their own, they can significantly amplify the impact of other vulnerabilities. The lack of a CVSS score doesn’t diminish the importance of applying the patch.
Possible Impact
The primary impact of CVE-2025-39665 is the disclosure of valid Checkmk usernames. This information can be leveraged by attackers for:
- Brute-Force Attacks: Knowing valid usernames reduces the search space for password cracking attempts.
- Credential Stuffing: If the enumerated usernames use the same credentials across multiple services, attackers can attempt to reuse compromised credentials.
- Social Engineering: Usernames can be used to personalize phishing attacks, increasing their effectiveness.
- Reconnaissance: Usernames provides attackers with more information about the target, assisting in attack planning.
Mitigation or Patch Steps
The recommended mitigation is to upgrade NagVis to version 1.9.48 or later. This version includes the necessary fix to address the user enumeration vulnerability.
- Upgrade NagVis: Download and install NagVis version 1.9.48 or a later version from the official NagVis website.
- Verify the Upgrade: After the upgrade, verify that the new version is running correctly.
- Monitor Logs: Monitor NagVis logs for any unusual activity or suspicious authentication attempts.
