GHSA-7w8c-qgxg-m7jx LibreNMS — Stored XSS via SNMP/Syslog Data in Legacy Templates

• Packagist librenms/librenms: < 26.5.0 → fixed in 26.5.0

Summary Multiple legacy PHP template files in LibreNMS directly output SNMP-sourced and syslog-sourced data into HTML without escaping. An attacker who controls a monitored network device (via compromised SNMP agent or syslog sender) can inject arbitrary JavaScript that executes when any authenticated LibreNMS user views the affected pages. Vulnerable Code Location 1: Syslog `program` field (clearest instance) File: `includes/html/print-syslog.inc.php:11,13` ```php $syslog_output .= '' . $entry['program'] . ' : ' . htmlspecialchars((string) $entry['msg']) . ''; ``` The `program` field is output without `htmlspecialchars()` while the adjacent `msg` field IS properly escaped. The `program` value comes from syslog messages received from monitored devices. Location 2: Alert details `ifAlias` (highest impact — main alerts page) File: `includes/html/functions.inc.php:607` ```php $fault_detail .= $tmp_alerts['ifAlias'] . '; '; ``` The `ifAlias` (port description) comes from SNMP polling and is stored in the `ports` table. When a port-related alert fires, `format_alert_details()` renders it unescaped. Multiple other fields in this function are also unescaped: `isisISAdjIPAddrAddress` (line 598), `service_desc`/`service_message` (lines 656,658), `bgpPeerDescr` (line 672), `mempool_descr` (line 686), `app_type` (line 709). Location 3: Health pages — `mempool_descr`, `storage_descr`, `sensor_descr` File: `includes/html/pages/device/health/mempool.inc.php:38` ```php echo "{$mempool->mempool_descr} ..."; ``` File: `includes/html/pages/device/health/storage.inc.php:27` ```php echo "{$drive['storage_descr']} ..."; ``` File: `includes/html/pages/device/health/sensors.inc.php:29` ```php echo "$sensor_descr ..."; ``` All three health page templates output SNMP-polled descriptions directly into `` tags without escaping. Location 4: Pseudowires `ifAlias` File: `includes/html/pages/pseudowires.inc.php:76` ```php echo "" . $pw_a['ifAlias'] . '' . $pw_b['ifAlias'] . ''; ``` Location 5: VRF page `ifAlias` File: `includes/html/pages/routing/vrf.inc.php:165` ```php echo "" . substr((string) short_port_descr($port['ifAlias']), 0, 22) . ''; ``` Data Flow ``` Attacker-controlled SNMP device/syslog source → SNMP polling stores ifAlias/mempool_descr/etc in DB (no sanitization on write) → OR syslog receiver stores program field in syslog table → Authenticated user views alerts/health/syslog page → Legacy PHP template echoes raw value into HTML → XSS executes in victim's browser session ``` Attack Scenario 1. Attacker compromises or controls a network device monitored by LibreNMS 2. Attacker configures the device's SNMP interface description (ifAlias) to: `` 3. LibreNMS polls the device via SNMP and stores the malicious ifAlias in the `ports` table 4. When any alert fires for this port, the XSS payload executes for every authenticated user viewing the alerts page 5. Alternatively: attacker sends syslog messages with XSS in the program field, targeting the syslog viewer page PoC Syslog vector (simplest) ```bash Send syslog message with XSS in program field Assuming LibreNMS syslog receiver is at 10.0.0.1:514 echo 'Mar 20 12:00:00 rogue-device : test message' | nc -u 10.0.0.1 514 ``` SNMP vector ```bash On attacker-controlled SNMP device, set interface description: snmpset -v2c -c private localhost IF-MIB::ifAlias.1 s '' LibreNMS will poll this during next discovery/polling cycle ``` Contrast with Properly Escaped Code Newer Blade templates and some legacy code properly escape SNMP data: • `includes/html/dev-overview-data.inc.php` uses `Clean::html()` for sysDescr, sysName, hardware • `app/Http/Controllers/Device/Tabs/PortsController.php` uses `htmlentities()` on ifAlias • `app/Http/Controllers/Table/EventlogController.php:97` uses `htmlspecialchars()` on message • All Blade templates use `{{ }}` auto-escaping The vulnerability exists specifically in the legacy `includes/html/` PHP files that have not been migrated to Blade.