CVE-2025-27026

Executive Summary

CVE-2025-27026 is a high-severity denial-of-service (DoS) vulnerability affecting Infinera G42 network equipment running firmware version R6.1.3. The flaw resides in the WebGUI interface, specifically in the CLI deactivation function. When an authenticated administrator deactivates the CLI via the WebGUI, the system fails to present a confirmation dialog (missing double-check feature). This action inadvertently disables not only the CLI but also the Linux Shell, WebGUI, and Physical Serial Console access. As a result, administrators lose all management interfaces, effectively bricking the device and requiring physical intervention or factory reset to regain control.

The vulnerability has a CVSS score of 4.9 (Medium), but its impact is severe due to the complete loss of device manageability. No public exploit code or proof-of-concept is available, and the vendor has not released a patch. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains high for organizations relying on Infinera G42 devices.

Supply Chain & Package Security

This vulnerability is not related to any software supply chain or package ecosystem (NPM, PyPI, Go, Ruby). It is a firmware-level issue in a proprietary network appliance.

CVSS Breakdown & Threat Level

• CVSS Score: 4.9 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: High (PR:H) – An attacker must have valid administrative credentials.
• User Interaction: None (UI:N) – No user action is needed beyond the attacker’s own.
• Scope: Unchanged (S:U) – The impact is confined to the vulnerable component.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: High (A:H) – Complete loss of device manageability.

Threat Level: Medium (due to high privileges required, but severe availability impact).

Deep Dive & Mechanics

The vulnerability is a classic case of CWE-358: Improperly Implemented Security Check for Standard. The WebGUI’s CLI deactivation function lacks a confirmation step (double-check). When an administrator clicks the deactivation button, the system immediately executes the command without asking for confirmation. The underlying script or API call that handles the deactivation is overly broad, affecting multiple services:

• CLI (Command Line Interface) – The primary management interface.
• Linux Shell – Backend shell access.
• WebGUI – The web-based management interface itself.
• Physical Serial Console – Direct console access.

The deactivation likely modifies systemd service states or iptables rules to block access. For example, it might stop sshd, lighttpd, and getty services, and flush firewall rules. Without a confirmation prompt, an administrator can accidentally trigger this, locking themselves out.

Root Cause: The deactivation function does not validate the scope of its action. It should only disable the CLI, but instead disables all management interfaces. The missing double-check (confirmation dialog) is the secondary flaw that prevents accidental activation.

Vulnerable vs. Patched Code

Since no patch is available, we can only infer the vulnerable code pattern. The vulnerable function likely looks like:

# Vulnerable pseudo-code
def deactivate_cli():
    # No confirmation check
    os.system("systemctl stop sshd")
    os.system("systemctl stop lighttpd")
    os.system("systemctl stop serial-getty@ttyS0")
    os.system("iptables -A INPUT -j DROP")
    return "CLI deactivated"

A patched version would include:

# Patched pseudo-code
def deactivate_cli():
    if not confirm_action("Are you sure you want to deactivate CLI? This will also disable other management interfaces."):
        return "Action cancelled"
    # Only stop CLI-related services
    os.system("systemctl stop sshd")
    return "CLI deactivated"

The patch should also scope the deactivation to only the CLI, not other interfaces.

Exploitation & Lab Setup

Red Team

Prerequisites: Valid administrative credentials to the Infinera G42 WebGUI.

Steps:

1. Log in to the WebGUI at https://<target-ip>/.
2. Navigate to the CLI deactivation page (likely under System > Management > CLI).
3. Click the "Deactivate CLI" button.
4. Observe that no confirmation dialog appears.
5. The device immediately becomes unresponsive to all management interfaces (CLI, WebGUI, SSH, serial console).

Impact: Complete denial of service. The device must be physically reset or reimaged.

Note: No public exploit code exists. This is a simple UI interaction.

Blue Team

Detection:

• Monitor for sudden loss of connectivity to Infinera G42 devices.
• Look for logs indicating CLI deactivation events (e.g., syslog entries like "CLI deactivated by admin").
• Use network monitoring to detect when a device stops responding to SNMP, SSH, or HTTP.

Prevention:

• Implement strict change management procedures for administrative actions.
• Use out-of-band management (e.g., console server) to maintain access.
• Apply vendor patch when available.
• Restrict WebGUI access to trusted IPs only.

Recovery:

• Physical access to the device is required. Perform a factory reset via the hardware reset button or console cable (if serial console is still accessible before deactivation).
• Reimage the device from a known good backup.

Indicators of Compromise (IOCs)

• Network: Sudden loss of HTTP/HTTPS, SSH, and SNMP responses from the device.
• Logs: Syslog entries containing "CLI deactivated" or "Management interfaces disabled".
• Process: Absence of sshd, lighttpd, or getty processes on the device.
• Firewall: iptables rules that drop all incoming traffic (e.g., -A INPUT -j DROP).

Detection Engineering

YARA Rule

rule CVE_2025_27026_Infinera_CLI_Deactivation {
    meta:
        description = "Detects log entries indicating CLI deactivation on Infinera G42"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-27026"
    strings:
        $log1 = "CLI deactivated" ascii wide nocase
        $log2 = "Management interfaces disabled" ascii wide nocase
        $log3 = "deactivate_cli" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Infinera G42 CLI Deactivation Event
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects when an administrator deactivates CLI on Infinera G42, potentially causing DoS
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-27026
logsource:
    product: infinera
    service: syslog
detection:
    selection:
        - "CLI deactivated"
        - "Management interfaces disabled"
    condition: selection
falsepositives:
    - Legitimate administrative actions (if confirmed)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-27026 Infinera G42 CLI Deactivation Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/deactivate_cli"; http_uri; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict WebGUI Access: Limit access to the WebGUI to trusted administrative IPs only using firewall rules.
2. Implement Change Management: Require two-person rule for any CLI deactivation actions.
3. Use Out-of-Band Management: Ensure console server or IPMI access is available as a fallback.

Long-Term Fix:

• Apply vendor patch when released. Monitor Infinera’s security advisories.
• Upgrade firmware to a version that includes a confirmation dialog and scoped deactivation.

Workaround:

• If possible, disable the CLI deactivation feature in the WebGUI configuration (if configurable).
• Use SSH or serial console for management instead of WebGUI.

Valters IT Signature: This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.