CVE-2023-38579

Executive Summary

CVE-2023-38579 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the Westermo Lynx 206-F2G industrial Ethernet switch. The vulnerability stems from a predictable or easily guessable CSRF token in the device's web management interface, allowing an attacker to craft malicious requests that, when triggered by an authenticated victim, cause unintended actions such as configuration changes or device reboots. The vulnerability carries a CVSS score of 8.0 (High) and, while no public exploit has been confirmed, the industrial networking context elevates the risk to operational technology (OT) environments. The vendor recommends hardening practices and notes that a fix was included in a later WeOS4 version.

Technical Analysis

Cross-Site Request Forgery (CSRF) is a vulnerability class that exploits the trust a web application holds in an authenticated user's browser. The attack mechanism relies on the application failing to adequately verify that a submitted request is intentional and initiated by the authenticated user, rather than a third-party malicious page.

In the case of CVE-2023-38579, the NVD description indicates that the CSRF token — the application's primary defense against this attack class — is "predictable or easily guessable." CSRF tokens are typically randomly generated values that must be validated on both the client-side (embedded in forms or headers) and server-side (on each state-changing request). When a token is generated using a weak entropy source, a static value, or a value derived from predictable data (e.g., timestamps, sequential numbers, or the session ID), an attacker can pre-compute valid tokens and embed them in a crafted request.

The affected device is the Westermo Lynx 206-F2G, an industrial Ethernet switch used in operational technology environments such as power utilities, transportation, and manufacturing. The device runs WeOS4, Westermo's operating system, which provides web-based management functionality. The attack surface is the web management interface, typically accessible over HTTP on the device's management port.

Because the flaw is in the CSRF token generation logic, the vulnerability is server-side. However, exploitation of CSRF requires the victim to have an active authenticated session with the device browser. The attacker's malicious page is hosted elsewhere and is loaded by the victim (via phishing, drive-by, or a compromised website). When the victim loads the page, JavaScript or auto-submitting forms trigger requests to the Lynx 206-F2G management interface, carrying the attacker's chosen payload (e.g., configuration modification, firmware downgrade, or account credential changes) along with the victim's valid session cookie and the predictable CSRF token generated by the attacker.

The lack of public PoC and the vendor's partial patch status suggest that knowledge of the vulnerability is partly limited to vendor research and coordinated disclosure. The EPSS score of 0.00232 (14.1% percentile) indicates a low probability of active exploitation in the wild, though this does not diminish the importance of remediation in OT contexts.

Insufficient technical detail available: The NVD description does not expose the specific token generation algorithm, endpoint names, or parameter names involved. The attack mechanism is therefore described at the vulnerability-class level.

Exploitation Scenarios

The attack chain for CVE-2023-38579 follows the standard CSRF exploitation pattern. No public PoC is available; the chain below is inferred from the vulnerability class.

Step 1 — Reconnaissance/Target Identification
The attacker identifies Westermo Lynx 206-F2G devices exposed to the internet or reachable within the OT network. Shodan and other search engines can identify these devices by their HTTP banner, login page fingerprint, or specific port signatures (typically TCP 80/443 for the web interface). The attacker also identifies an authenticated user (e.g., a network administrator) who manages the device. This user may be targeted via spear-phishing or by compromising a website they are known to visit.

Step 2 — Triggering the Flaw
Given that the CSRF token is predictable, the attacker generates a valid token value using the same algorithm and generation parameters as the target device. The attacker then constructs an HTML page containing an auto-submitting form or JavaScript that issues a state-changing HTTP request to the Lynx 206-F2G management interface. The request includes the attacker's generated CSRF token and is designed to execute a specific management action (e.g., altering network configuration, changing administrative credentials, or rebooting).

Step 3 — Payload/Execution
The victim, while authenticated to the Lynx 206-F2G, is tricked into visiting the malicious page. The page silently issues the crafted request. Because the victim's browser holds a valid session cookie and the token is validated as "correct" by the server (since the attacker guessed it), the server processes the request as if it were a legitimate action by the authenticated user.

Step 4 — Post-Exploitation Impact
Depending on the action executed, the impact can range from denial of service (device reboot or network reconfiguration causing loss of connectivity) to persistent compromise (attacker-modified configuration that redirects traffic, disables security controls, or establishes a foothold for further lateral movement into the OT network). In the worst case, the attacker can change administrative credentials, locking legitimate operators out while retaining access themselves.

Impact Assessment

The CVSS score of 8.0 (High) reflects the serious implications of a CSRF vulnerability in an industrial networking component. Key factors contributing to this score include the network attack vector (N), the low attack complexity (L), the potential for high confidentiality, integrity, and availability impact, and the requirement for user interaction.

Business Impact: For organizations operating in critical infrastructure sectors, unauthorized modification of an Ethernet switch's configuration can directly disrupt industrial processes. A simple reboot of the Lynx 206-F2G could isolate a section of the network, causing downtime in production lines or affecting safety systems. More sophisticated attacks could manipulate network traffic routing to enable further intrusion, altering SCADA or ICS data flows.

Affected Systems: The Lynx 206-F2G is a managed industrial Ethernet switch with a web-based management interface. Any device running WeOS4 versions prior to the patched revision is affected. Given the lack of a confirmed official patch, the blast radius includes all deployed devices until the vendor's later WeOS4 version is verified and deployed by the organization.

Blast Radius: The vulnerability is exploitable by an unauthenticated remote attacker, but requires the victim to be authenticated to the device browser. This reduces the immediate attack surface to scenarios where the attacker can coerce an authenticated user into loading a malicious page. However, in OT environments where management workstations are shared or where administrators routinely browse the internet from the same machine used for device management, the risk is magnified.

Detection Guidance

Sigma Rule

title: Suspicious HTTP Request to Westermo Lynx Device with Predictable CSRF Token
id: 8a3c9e6f-2d4b-4f7a-9c1e-5d8b3a2f1c0e
status: experimental
description: Detects HTTP requests to a Westermo Lynx 206-F2G management interface that may indicate CSRF token guessing attempts.
author: Valtersit Threat Intelligence
date: 2023/10/01
logsource:
  category: webserver
  product: westermo
detection:
  selection:
    c-uri|contains:
      - '/config'
      - '/reboot'
      - '/admin'
    csrf_token|re: '^[a-f0-9]{6,12}$'  # Weak token pattern (short hex)
  condition: selection
level: high
tags:
  - attack.t1204.001
  - attack.t1190
  - cve.2023.38579

YARA Rule

rule Westermo_Lynx_CSRF_Token_Exploit {
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detect HTML/JavaScript payloads attempting CSRF against Westermo Lynx devices with predictable tokens"
        cve = "CVE-2023-38579"
        date = "2023-10-01"
        score = 60
    strings:
        $ip_pattern = /10\.\d{1,3}\.\d{1,3}\.\d{1,3}/  // Common private IP ranges for OT
        $login_page = "login" ascii nocase
        $reboot = "reboot" ascii nocase
        $form_js = "autosubmit" ascii nocase
        $token_param = "token" ascii nocase
    condition:
        filesize < 50KB
        and 3 of them
}

Suricata IDS Rule

alert http any any -> $WESTERMO_DEVICES any (msg:"CVE-2023-38579 - Westermo Lynx CSRF Token Guessing Attempt"; flow:established,to_server; http.uri; content:"/admin"; http.uri; content:"token="; http.uri; pcre:"/token=[a-f0-9]{6,12}/I"; sid:5000001; rev:1; reference:cve,2023-38579; classtype:attempted-admin;)

Elastic Detection

sequence by source.ip, destination.ip with maxspan=5m
  [http where url.path == "/admin" and url.query contains "token="]
  [http where url.path in ("/reboot", "/config", "/admin")
   and http.response.status_code == 200]

Splunk SPL Query

index=web sourcetype=access_combined_w3c 
| search "/admin" OR "/reboot" OR "/config"
| regex _raw="token=[a-f0-9]{6,12}"
| stats count by src_ip, dest_ip, uri, method, status
| where count > 3

Wazuh OSSEC Rule

<group name="westermo,">
  <rule id="100401" level="10">
    <decoded_as>json</decoded_as>
    <field name="url">\.(admin|reboot|config).*token=</field>
    <description>Westermo Lynx CSRF token evasion attempt detected</description>
    <group>web_application_attack,</group>
    <mitre>
      <id>T1204.001</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 1/4 (PARTIAL) — No official fix has been confirmed. The vendor notes that the vulnerability was patched in a later WeOS4 version, but no specific version number is provided, and no patch source is confirmed.

1. Immediate Mitigations:

• Restrict network access to the Lynx 206-F2G web management interface. Use VLANs, firewall rules, or access control lists to ensure that only trusted management workstations can reach the device.
• Disable the web management interface if not strictly necessary; use CLI over SSH or serial console instead.
• Disable all unused services on the device (attack surface reduction), as recommended by the vendor.
• Ensure administrators do not browse the internet from the same workstation used to manage OT devices.

2. Patch/Upgrade Steps:

• Contact Westermo support or monitor their security advisory portal for the exact WeOS4 version containing the CSRF fix.
• Once identified, schedule a maintenance window to upgrade the device firmware in a controlled staging environment before deployment to production.

3. Long-Term Hardening:

• Enforce the use of strong, non-guessable session tokens through the vendor's configuration options if available.
• Implement network segmentation between corporate IT networks and OT networks to reduce the likelihood of administrators visiting malicious pages while authenticated to device management interfaces.
• Deploy a web application firewall (WAF) or IDS/IPS in front of management interfaces to monitor for anomalous HTTP requests.
• Harden the administrator browser with extensions that block third-party requests to internal IP ranges (e.g., NoScript, Content Security Policy).

References

1. NVD Entry for CVE-2023-38579 — https://nvd.nist.gov/vuln/detail/CVE-2023-38579
2. Westermo Security Advisory (vendor) — WeOS4 release notes and hardening guidance (contact vendor for specific advisory document)
3. ATT&CK Technique T1204.001 — User Execution: Malicious Link — https://attack.mitre.org/techniques/T1204/001/
4. ATT&CK Technique T1190 — Exploit Public-Facing Application — https://attack.mitre.org/techniques/T1190/

Threat Actor Activity: No known threat actor campaigns or exploit-in-the-wild evidence associated with this CVE is available. The EPSS score of 0.00232 indicates a very low probability of current exploitation. The CISA KEV catalog does not include this CVE.