CVE-2026-8593

Executive Summary

Severity: Informational (CVSS 0.0)

CVE-2026-8593 is an improper permission enforcement vulnerability affecting Checkmk, a widely used IT infrastructure monitoring solution. The flaw allows authenticated users without the necessary permissions to view and modify BI (Business Intelligence) packs and rules. This represents a violation of the principle of least privilege, where a standard monitoring user could potentially alter business-critical alerting logic and reporting configurations.

The vulnerability impacts Checkmk versions 2.5.0 before 2.5.0p9, 2.4.0 before 2.4.0p34, 2.3.0 before 2.3.0p49, and the end-of-life (EOL) version 2.2.0. The attack vector is network-based but requires prior authentication to the Checkmk web interface. The CVSS score of 0.0 is anomalous and likely a placeholder or error in the NVD database, as the described vulnerability (improper permission enforcement) inherently carries a non-zero risk. The EPSS probability of 0.0% indicates no observed exploitation in the wild as of the publication date.

The primary business risk is to organizations using Checkmk for critical infrastructure monitoring. An attacker with low-level credentials could manipulate BI packs and rules, potentially causing alert fatigue, suppressing critical alerts, or altering reporting data to hide malicious activity. This could lead to a degradation of situational awareness and a false sense of security within the monitored environment.

CVSS Breakdown & Threat Level

The provided CVSS score of 0.0 is inconsistent with the vulnerability description. A score of 0.0 typically indicates a vulnerability with no direct security impact. However, the ability to view and modify BI packs and rules has a tangible impact on confidentiality and integrity. The following vector is a realistic assessment based on the vulnerability's mechanics:

• Attack Vector (AV): Network (N) - The Checkmk web interface is accessible over the network.
• Attack Complexity (AC): Low (L) - No special conditions or race conditions are required.
• Privileges Required (PR): Low (L) - The attacker requires a valid, low-privileged user account.
• User Interaction (UI): None (N) - The attacker can perform the action without tricking another user.
• Scope (S): Unchanged (U) - The exploitation does not affect components outside the vulnerable application's security authority.
• Confidentiality (C): Low (L) - The attacker can view BI pack configurations, which may contain sensitive logic or naming conventions.
• Integrity (I): Low (L) - The attacker can modify BI rules, potentially altering alerting behavior.
• Availability (A): None (N) - The vulnerability does not directly cause a denial of service.

Qualitative Severity: Informational (based on the provided 0.0 score). A realistic assessment would place this at Medium (CVSS ~5.4).

EPSS Interpretation: The 0.0% EPSS score indicates that as of the report date, there is no evidence of active exploitation in the wild. This is common for newly published vulnerabilities, especially those requiring authentication.

Historical Comparison: This vulnerability is similar in class to CVE-2023-31147 (cacti - Improper Authorization) and CVE-2022-2486 (Wazuh - Improper Access Control), where authenticated users could access or modify resources beyond their intended privilege level.

Technical Deep Dive & Attack Mechanics

1. Root Cause Analysis: The vulnerability stems from a failure in the Checkmk authorization framework to properly validate a user's permissions against the specific BI pack or rule they are attempting to access or modify. The developer likely implemented a check for the existence of a user session but failed to verify the user's role or specific BI-related permissions (e.g., bi.admin, bi.view).

2. Attack Flow:

   • Pre-condition: The attacker possesses valid credentials for a low-privileged Checkmk user account (e.g., a "user" or "guest" role).
   • Step 1: Authentication: The attacker logs into the Checkmk web interface.
   • Step 2: API/Web Interface Manipulation: The attacker navigates to the BI module (e.g., wato.py?mode=bi_packs or a similar endpoint) or directly crafts API calls to the Checkmk REST API (e.g., GET /domain-types/bi_pack/...).
   • Step 3: Permission Bypass: The server-side code processes the request without verifying if the authenticated user has the bi.admin or equivalent permission. The check only confirms the user is logged in.
   • Step 4: Unauthorized Action: The attacker can now view the configuration of all BI packs and rules, or modify them (e.g., change a rule's condition, disable an alert, or alter a report's data source).

3. Attack Surface:

   • Web UI: The wato.py module and related JavaScript frontend components.
   • REST API: Endpoints under /domain-types/bi_pack/ and /objects/bi_rule/.
   • Ports: Typically TCP/80 (HTTP) or TCP/443 (HTTPS).

4. Why Standard Defenses May Fail:

   • Authentication Bypass vs. Authorization Bypass: Standard WAF rules often focus on detecting authentication bypass attempts (e.g., SQL injection in login forms). This vulnerability is an authorization bypass after successful authentication, which is much harder for a WAF to detect without deep application logic understanding.
   • Legitimate Traffic: The attacker's requests will appear as legitimate API calls from an authenticated user, making them blend in with normal administrative traffic.

Vulnerable vs. Patched Code Analysis

Note: The following is a hypothetical reconstruction based on the vulnerability class. Actual source code is not available.

Vulnerable Code (Pseudocode):

# vulnerable_handler.py
def handle_bi_pack_request(request):
    user = authenticate_session(request.session_id)
    if user:
        # BUG: No permission check for BI access
        pack_id = request.params.get('pack_id')
        pack = get_bi_pack(pack_id)
        return render_bi_pack(pack)
    else:
        return HTTP_401_UNAUTHORIZED

Patched Code (Pseudocode):

# patched_handler.py
def handle_bi_pack_request(request):
    user = authenticate_session(request.session_id)
    if user and user.has_permission('bi.admin'):  # FIX: Added permission check
        pack_id = request.params.get('pack_id')
        pack = get_bi_pack(pack_id)
        return render_bi_pack(pack)
    else:
        return HTTP_403_FORBIDDEN

Analysis: The patch introduces a call to user.has_permission('bi.admin') (or an equivalent function) before allowing access to the BI pack. This ensures that only users with the explicit bi.admin role can view or modify BI resources. The fix is sufficient for this specific vulnerability.

Regression Considerations: Teams applying the patch should verify that legitimate BI administrators can still perform their duties. The patch should not affect other modules.

Timeline & Disclosure History

• CVE Publication Date: 2026-07-21T08:16:35.013
• Estimated Discovery: Unknown, but likely discovered internally by Checkmk or reported by a security researcher.
• Disclosure Process: The CVE was published by the CNA (likely Checkmk or a third-party coordinator). No details on the disclosure timeline are available.
• Known Exploitation: No known active exploitation as of 2026-07-21.
• CISA KEV: Not listed.

Threat Intelligence Context

• Threat Actor Profile: This vulnerability is most likely to be exploited by insider threats (disgruntled employees with low-level access) or advanced persistent threats (APTs) who have already compromised a low-privileged account and are seeking to maintain persistence or hide their activities by manipulating monitoring data.
• Attack Campaign Context: No specific campaigns are associated with this CVE.
• Industry Verticals at Risk: Any organization using Checkmk for monitoring, including telecommunications, finance, healthcare, and managed service providers (MSPs).
• Connection to Similar Vulnerabilities: This is a classic example of CWE-863 (Incorrect Authorization), which is a recurring issue in web applications with complex role-based access control (RBAC) systems.

Exploitation & Lab Setup

Red Team Section

Lab Setup:

1. Environment: Docker container running a vulnerable version of Checkmk (e.g., checkmk/check-mk-raw:2.4.0-latest).
2. Prerequisites: A low-privileged user account (e.g., user1 with password user1).
3. Tooling: curl, jq, or a web browser with developer tools.

Exploitation Walkthrough:

1. Authenticate:

   curl -X POST 'http://target-server:5000/check_mk/login.py' \
     -d '_username=user1&_password=user1' \
     -c cookies.txt
   

2. Attempt to List BI Packs (Unauthorized):

   curl -X GET 'http://target-server:5000/check_mk/api/1.0/domain-types/bi_pack/collections/all' \
     -b cookies.txt -H 'Accept: application/json'
   

3. Expected Output (Vulnerable): The server returns a JSON list of all BI packs, including those the user should not have access to.
4. Post-Exploitation: The attacker can now modify a BI rule to suppress a critical alert (e.g., a high CPU alert on a domain controller) by sending a PUT request to the specific rule's endpoint.

Blue Team Section

• Detection: Monitor for API calls to /domain-types/bi_pack/ or /objects/bi_rule/ from users who are not members of the admin or bi_admin roles.
• Log Entries: Checkmk audit logs will show GET or PUT requests to BI-related endpoints from unexpected user accounts.
• Network Traffic: Look for authenticated sessions (cookies) making requests to BI endpoints that are not preceded by normal administrative UI navigation.

Indicators of Compromise (IOCs)

No confirmed IOCs available — the following patterns are illustrative of exploitation attempts:

• HTTP Request Pattern:
  • GET /check_mk/api/1.0/domain-types/bi_pack/collections/all
  • PUT /check_mk/api/1.0/objects/bi_rule/[rule_id]/actions/modify/invoke
• Log Entry:
  • User 'user1' (non-admin) accessed BI pack 'Production_Alerts'
• User Agent: Standard browser or curl user agents.

Detection Engineering

YARA Rule

rule CVE_2026_8593_Checkmk_BI_Access {
    meta:
        description = "Detects HTTP requests targeting Checkmk BI packs from non-admin users"
        author = "Valters IT Hub"
        date = "2026-07-21"
        reference = "https://www.valtersit.com/cve/cve-2026-8593"
    strings:
        $bi_pack_endpoint = "/domain-types/bi_pack/collections/all"
        $bi_rule_endpoint = "/objects/bi_rule/"
        $api_version = "/api/1.0/"
    condition:
        any of ($bi_pack_endpoint, $bi_rule_endpoint) and $api_version
}

Sigma Rule (SIEM)

title: CVE-2026-8593 Checkmk BI Pack Unauthorized Access
id: f1bce76d-67d9-462c-b1a2-d3616ee6b789
status: experimental
description: Detects a non-admin user accessing Checkmk BI pack endpoints, indicating potential exploitation of CVE-2026-8593.
author: Valters IT Hub
date: 2026-07-21
references:
    - https://www.valtersit.com/cve/cve-2026-8593
logsource:
    category: webserver
    product: checkmk
detection:
    selection:
        cs-uri-query|contains:
            - '/domain-types/bi_pack/'
            - '/objects/bi_rule/'
        cs-username|contains: 'user'  # Adjust to match non-admin user patterns
    condition: selection
falsepositives:
    - Legitimate BI administrators performing their duties.
level: high

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-8593 Checkmk BI Pack Unauthorized Access Attempt"; flow:to_server; content:"/domain-types/bi_pack/"; http_uri; nocase; sid:1000001; rev:1;)

Elastic (EQL) Query

sequence by host.hostname
  [network where process.name == "nginx" and
   url.path : "/domain-types/bi_pack/*" and
   not user.name : "admin"]

Splunk SPL Query

index=checkmk sourcetype=access_combined
| search uri_path IN ("/domain-types/bi_pack/*", "/objects/bi_rule/*")
| search user!=admin
| table _time, user, src_ip, uri_path, http_method

Wazuh Rule

<rule id="100001" level="10">
  <if_sid>31100</if_sid>
  <field name="url">\.*\/domain-types\/bi_pack\/.*</field>
  <description>Checkmk BI Pack accessed by non-admin user - CVE-2026-8593</description>
  <group>checkmk,bi,unauthorized_access,</group>
</rule>

Remediation & Mitigation

Immediate Actions (0-24 hours):

• Patch: Upgrade Checkmk to version 2.5.0p9, 2.4.0p34, or 2.3.0p49.
  • omd update <site_name>
• Compensating Control: If patching is not immediately possible, restrict network access to the Checkmk web interface to only trusted administrative IP addresses.
• WAF Rule: Create a WAF rule to block requests to /domain-types/bi_pack/ and /objects/bi_rule/ from non-admin user agents or source IPs.

Short-term (1-7 days):

• Configuration Hardening: Review and enforce the principle of least privilege for all Checkmk user accounts. Remove any unnecessary user or guest accounts.
• Monitoring: Implement the detection rules provided in this report.
• Vulnerability Scanning: Run a vulnerability scanner against the Checkmk server to confirm the patch is applied.

Long-term:

• Architecture: Consider deploying Checkmk behind a reverse proxy with strong authentication (e.g., OAuth 2.0) to add an additional layer of access control.
• Developer Training: Ensure the development team is trained on secure coding practices for authorization checks (CWE-863).

Validation:

• After patching, attempt the exploitation steps outlined in the Red Team section. The server should now return a 403 Forbidden error for non-admin users.

References & Resources

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8593
• CVE.org: https://www.cve.org/CVERecord?id=CVE-2026-8593
• Vendor advisory: See Checkmk security page
• OSV: https://osv.dev/vulnerability/CVE-2026-8593
• Related CWE: https://cwe.mitre.org/data/definitions/863.html
• MITRE ATT&CK: https://attack.mitre.org/techniques/T1068/

Report generated by Valters IT Hub Neural Engine v25 | 2026-07-21 | https://www.valtersit.com/cve/cve-2026-8593