CVE-2025-2596

Q: How do I fix CVE-2025-2596?

1. Backup your Checkmk configuration. 2. Update to patched version using 'omd update' command. 3. Restart Checkmk services. 4. Verify the update completed successfully.

Q: What is the severity of CVE-2025-2596?

CVE-2025-2596 has a CVSS score of 5.3 (MEDIUM). This vulnerability in Checkmk allows attackers to bypass session logout mechanisms, potentially maintaining unauthorized access to monitoring systems. It affects Checkmk versions before 2.3.0p30, 2.2.0p41, and 2.1.0p49. Organizations using these vulnerable versions are at risk of session hijacking.

5.3 MEDIUM

Authentication Bypass

📋 TL;DR

This vulnerability in Checkmk allows attackers to bypass session logout mechanisms, potentially maintaining unauthorized access to monitoring systems. It affects Checkmk versions before 2.3.0p30, 2.2.0p41, and 2.1.0p49. Organizations using these vulnerable versions are at risk of session hijacking.

💻 Affected Systems

Products:

Checkmk GmbH Checkmk

Versions: Versions <2.3.0p30, <2.2.0p41, and 2.1.0p49 (EOL)

Operating Systems: Linux-based systems running Checkmk

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations of affected versions are vulnerable. Checkmk 2.1.0 series is End of Life (EOL).

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Attackers maintain persistent unauthorized access to Checkmk monitoring dashboards, potentially viewing sensitive infrastructure data, modifying monitoring configurations, or using the system as a pivot point for further attacks.

🟠

Likely Case

Unauthorized users maintain access to monitoring interfaces after logout attempts, allowing continued viewing of system metrics and potentially limited configuration changes.

🟢

If Mitigated

With proper session management controls and network segmentation, impact is limited to unauthorized viewing of monitoring data without system compromise.

🌐 Internet-Facing: MEDIUM - Internet-facing Checkmk instances could allow external attackers to maintain unauthorized access, but exploitation requires initial authentication.

🏢 Internal Only: MEDIUM - Internal attackers with valid credentials could maintain persistent access beyond intended logout, potentially accessing sensitive monitoring data.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires valid user credentials initially. The vulnerability involves session management flaws that could be exploited through crafted requests.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 2.3.0p30, 2.2.0p41, or 2.1.0p49

Vendor Advisory: https://checkmk.com/werk/17808

Restart Required: Yes

Instructions:

1. Backup your Checkmk configuration. 2. Update to patched version using 'omd update' command. 3. Restart Checkmk services. 4. Verify the update completed successfully.

🔧 Temporary Workarounds

Session Timeout Reduction

linux

Reduce session timeout values to limit potential unauthorized access window

omd config set APACHE session_timeout 900

Network Access Restriction

linux

Restrict Checkmk access to trusted networks only

ufw allow from 192.168.1.0/24 to any port 80,443 proto tcp

🧯 If You Can't Patch

Implement strict network segmentation to isolate Checkmk instances
Enforce multi-factor authentication for all Checkmk user accounts

🔍 How to Verify

Check if Vulnerable:

Check Checkmk version with 'omd version' command and compare against affected versions

Check Version:

omd version

Verify Fix Applied:

Verify version is 2.3.0p30 or higher, 2.2.0p41 or higher, or exactly 2.1.0p49

📡 Detection & Monitoring

Log Indicators:

Multiple successful logins from same user in quick succession
Session IDs persisting beyond logout events

Network Indicators:

Unusual session duration patterns
Requests to session endpoints after logout

SIEM Query:

source="checkmk" AND (event="session_persist" OR event="logout_bypass")

📊 Metadata

CVE ID: CVE-2025-2596

CVSS v3 Score: 5.3 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CWE: CWE-613

EPSS Score: 0.08% exploit probability (23.1th percentile)

Published: March 26, 2025

Last Updated: August 25, 2025

🔗 References

https://checkmk.com/werk/17808 Vendor Advisory

📋 TL;DR

💻 Affected Systems

📦 What is this software?

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