CVE-2026-109352 in LibreNMS
Summary
by MITRE • 10/12/2026
LibreNMS before 26.9.0 contains a stored cross-site scripting vulnerability in includes/html/pages/device/wireless.inc.php, which echoes wireless sensor sensor_descr values, populated from SNMP DisplayString fields during discovery, into HTML without escaping. Attackers controlling a monitored device's SNMP agent can set values such as AI-AP-MIB::aiSSID to malicious JavaScript that executes when authenticated users view the device's Wireless tab, enabling session hijacking.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in LibreNMS versions prior to 26.9.0 represents a critical stored cross-site scripting flaw located within the wireless monitoring interface, specifically in the file includes/html/pages/device/wireless.inc.php. This security defect arises from an improper neutralization of special elements during data processing, where the application fails to properly validate or escape user-controllable input before including it in web pages. The root cause lies in how LibreNMS handles SNMP discovery processes for wireless sensors. During network discovery, the system queries monitored devices using Simple Network Management Protocol (SNMP) and retrieves specific DisplayString fields, such as AI-AP-MIB::aiSSID, which typically contain descriptive text like Wi-Fi network names. These values are stored directly in the database without sufficient sanitization. When an authenticated user subsequently navigates to the Wireless tab for a device that has been compromised or configured with malicious SNMP responses, the application echoes these unescaped sensor descriptions directly into the HTML output. This behavior allows any JavaScript code embedded within those strings to execute within the context of the victim's browser session, effectively bypassing standard same-origin policies and client-side security controls.
From an operational perspective, this vulnerability poses a severe risk to network monitoring infrastructure integrity. Because the malicious payload is stored in the database rather than being passed via URL parameters or form submissions, it persists until manually removed from the configuration of the monitored device. This persistence ensures that every authenticated user who views the affected wireless interface will trigger the execution of the injected script. The primary impact involves session hijacking and credential theft. An attacker controlling a managed network device can craft SNMP responses containing malicious JavaScript payloads. When an administrator or operator logs into LibreNMS to monitor their infrastructure, they inadvertently execute this code in their browser context. This enables the extraction of sensitive information such as authentication cookies, tokens, or other session identifiers, allowing the attacker to impersonate the victim and gain unauthorized access to the monitoring platform. Furthermore, depending on the specific payload delivered by the attacker, it could facilitate further attacks within the internal network, including phishing for additional credentials or pivoting to other web applications accessible from the same browser session.
This vulnerability aligns with Common Weakness Enumeration (CWE) ID 79, which classifies Improper Neutralization of Input During Web Page Generation known as Cross-site Scripting. The attack vector is categorized under CWE-613 for Insufficient Session Expiration and CWE-20 for Improper Input Validation. In terms of the MITRE ATT&CK framework, this exploit maps to Taint Analysis failures in input validation and specifically relates to techniques involving Stored XSS (Tactic: Execution or Collection). The attacker leverages their control over a managed asset to inject malicious content into a trusted application's data store, exploiting the trust relationship between the LibreNMS server and its authenticated users. This scenario highlights the danger of trusting SNMP responses from potentially compromised endpoints without rigorous validation, as network management tools often operate with high privileges and access to sensitive operational data.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The most effective solution is to upgrade LibreNMS to version 26.9.0 or later, where the developers have implemented proper output encoding for wireless sensor descriptions before rendering them in HTML contexts. For environments unable to patch immediately, administrators should implement strict input validation on SNMP agents by restricting which MIB OIDs are queried and ensuring that only alphanumeric characters and standard punctuation are accepted as valid values for descriptive fields like SSID names. Additionally, deploying a Web Application Firewall (WAF) with rules capable of detecting and blocking XSS payloads in HTTP responses can provide an additional layer of defense. It is also critical to enforce strong authentication mechanisms such as multi-factor authentication to reduce the impact if session tokens are compromised. Regular audits of SNMP configurations on managed devices should be conducted to ensure that no unauthorized changes have been made to community strings or agent settings, thereby preventing attackers from injecting malicious data during future discovery cycles.