Unauthenticated username enumeration via distinct cookie failures
Published Dec 3, 2025 · Updated Dec 3, 2025
User enumeration in NagVis Checkmk MultisiteAuth before 1.9.48 allows remote attackers to identify valid Checkmk usernames. CoreLogonMultisite::checkAuthCookie looked up the supplied cookie username in local authentication files and produced a distinct user-not-found failure before uniform Checkmk session validation. No authentication or user interaction is required, and the disclosed consequence is limited to learning which Checkmk accounts exist.
Summary
What happened
User enumeration in NagVis Checkmk MultisiteAuth before 1.9.48 allows remote attackers to identify valid Checkmk usernames. CoreLogonMultisite::checkAuthCookie looked up the supplied cookie username in local authentication files and produced a distinct user-not-found failure before uniform Checkmk session validation. No authentication or user interaction is required, and the disclosed consequence is limited to learning which Checkmk accounts exist.
The record
- CVE
- CVE-2025-39665
- Published
- Dec 3, 2025
- Updated
- Dec 3, 2025
- Vendor
- NagVis Project
- Product
- NagVis
- Classifications
- CWE-203, CAPEC-575, T1087
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Dec 3, 2025CVE publishedPublication date reported by the CVE source.
- Dec 3, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=1.9.0 <1.9.48
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo