CVE-2026-33457

Executive Summary

CVE-2026-33457 is a Livestatus injection vulnerability in Checkmk, an open-source IT monitoring solution. The flaw resides in the prediction graph page, where insufficient sanitization of the service description value allows an authenticated attacker to inject arbitrary Livestatus commands via a crafted service name parameter. This can lead to unauthorized data access, manipulation of monitoring data, or potential lateral movement within the monitored environment. The vulnerability affects versions prior to 2.5.0b4, 2.4.0p26, and 2.3.0p47. A patch is available, and immediate upgrade is recommended.

CVSS Breakdown & Threat Level

• CVSS Score: 6.3 (Medium)
• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): Low (L)
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): Low (L)
• Integrity (I): Low (L)
• Availability (A): Low (L)

The medium severity reflects the requirement for authentication, but the low attack complexity and network-based vector make it a viable target for authenticated attackers.

Deep Dive & Mechanics

The vulnerability is a Livestatus injection, a variant of command injection specific to Checkmk's Livestatus protocol. Livestatus is a query language used to retrieve monitoring data from Checkmk's core. The prediction graph page constructs a Livestatus query using user-supplied service name parameters without proper sanitization. An attacker can inject additional Livestatus commands by crafting a malicious service name, such as appending ; or | followed by arbitrary Livestatus commands.

The injection occurs because the service description value is directly concatenated into a Livestatus query string. For example, a request like:

/prediction_graph.py?service=valid_service;rm+important_file

could result in the execution of rm important_file on the monitoring server, depending on the context.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

# Vulnerable: Direct concatenation of user input
query = "GET services\nColumns: service_description\nFilter: service_description = " + user_input
result = livestatus.query(query)

Patched Code (Conceptual):

# Patched: Input sanitization and parameterized queries
from livestatus import sanitize
safe_input = sanitize(user_input)
query = "GET services\nColumns: service_description\nFilter: service_description = " + safe_input
result = livestatus.query(query)

The patch introduces a sanitization function that escapes or rejects malicious characters, preventing injection.

Exploitation & Lab Setup

Red Team

1. Setup: Deploy a vulnerable Checkmk instance (e.g., version 2.3.0p46) in a lab environment.
2. Authentication: Obtain valid credentials for a low-privileged user.
3. Craft Payload: Create a malicious service name parameter, e.g., service=valid_service;rm /tmp/test.
4. Send Request: Use curl or a script to send a GET request to the prediction graph page:

   curl -u "user:password" "http://target/checkmk/prediction_graph.py?service=valid_service;rm+/tmp/test"
   

5. Verify: Check if the command executed (e.g., file deletion).

Blue Team

1. Monitor Logs: Look for unusual service name parameters in web server logs (e.g., Apache access logs).
2. Detect Anomalies: Use SIEM rules to flag requests containing special characters like ;, |, or & in the service parameter.
3. Network Analysis: Monitor for unexpected Livestatus queries or outbound connections from the Checkmk server.
4. Honeypot: Deploy a fake service name that triggers an alert when accessed.

Indicators of Compromise (IOCs)

• Web Logs: Requests to /checkmk/prediction_graph.py with service parameter containing special characters (e.g., ;, |, &).
• System Logs: Unexpected command execution logs (e.g., rm, wget, curl).
• File System: Unauthorized file modifications or deletions in /tmp or other writable directories.
• Network: Outbound connections from the Checkmk server to unknown IPs (potential C2).

Detection Engineering

YARA Rule

rule CVE_2026_33457_Livestatus_Injection {
    meta:
        description = "Detects Livestatus injection attempts in Checkmk prediction graph page"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-33457"
    strings:
        $injection = /service=[^&]*[;|&]/
    condition:
        $injection
}

Sigma Rule

title: Checkmk Livestatus Injection Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit CVE-2026-33457 via malicious service parameter
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: 
            - 'service='
            - ';'
            - '|'
            - '&'
    condition: selection
falsepositives:
    - Legitimate use of special characters in service names (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-33457 Checkmk Livestatus Injection Attempt"; flow:to_server; content:"/checkmk/prediction_graph.py"; http_uri; content:"service="; http_uri; pcre:"/service=[^&]*[;|&]/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade to Checkmk 2.5.0b4, 2.4.0p26, or 2.3.0p47.
2. Workaround: If upgrade is not possible, restrict access to the prediction graph page to trusted users only via web server ACLs.
3. Network: Place Checkmk behind a reverse proxy with input validation.
4. Monitoring: Enable detailed logging for the prediction graph page and alert on suspicious parameters.
5. Least Privilege: Ensure users have minimal necessary permissions.

Valters IT

{/* [Security Hash: E9400A3DBCCC60F0A5B0712D] */}