CVE-2025-66956

Executive Summary

CVE-2025-66956 is a critical Insecure Access Control vulnerability in Asseco SEE Live 2.0, specifically affecting the Contact Plan, E-Mail, SMS, and Fax components. The vulnerability allows remote, unauthenticated attackers to access and execute arbitrary attachments via a computable URL, leading to full system compromise. With a CVSS score of 9.9, this vulnerability poses an extreme risk to organizations using this software. No patch is currently available, and no public proof-of-concept (PoC) or exploit code has been released. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the severity demands immediate attention.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a proprietary enterprise software component from Asseco SEE. Organizations should verify the integrity of their Asseco SEE Live 2.0 installations and monitor for any unofficial patches or updates.

CVSS Breakdown & Threat Level

• CVSS Score: 9.9 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability affects only the vulnerable component.
• Confidentiality Impact: High (C:H) – Full data access.
• Integrity Impact: High (I:H) – Full data modification.
• Availability Impact: High (A:H) – Full system disruption.

Threat Level: Critical. Immediate action required.

Deep Dive & Mechanics

The vulnerability resides in the URL handling logic of Asseco SEE Live 2.0's Contact Plan, E-Mail, SMS, and Fax components. The application fails to properly validate access control when processing URLs that reference attachments. An attacker can craft a predictable URL pattern (e.g., /attachment?id=12345) to enumerate and access attachments without authentication. This allows the attacker to:

1. Access sensitive data – Read emails, SMS messages, faxes, and contact plans.
2. Execute attachments – If the application processes attachments (e.g., opening files), the attacker can trigger execution of malicious content.
3. Escalate privileges – By accessing administrative attachments or configuration files.

The root cause is a missing authorization check in the URL routing mechanism. The application trusts the URL parameter without verifying the user's session or permissions.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable pattern.

Vulnerable Code (Conceptual):

# Vulnerable: No access control check
@app.route('/attachment')
def get_attachment():
    attachment_id = request.args.get('id')
    # Directly returns attachment without authentication
    return send_file(f'/attachments/{attachment_id}')

Patched Code (Hypothetical):

# Patched: Access control enforced
@app.route('/attachment')
@login_required
def get_attachment():
    attachment_id = request.args.get('id')
    if not current_user.can_access(attachment_id):
        abort(403)
    return send_file(f'/attachments/{attachment_id}')

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• Target: Asseco SEE Live 2.0 instance (e.g., http://target:8080)
• Attacker: Kali Linux with curl, Burp Suite, or custom scripts.

Exploitation Steps:

1. Enumerate attachment IDs – Use a simple loop to guess IDs.

   for i in $(seq 1 1000); do
       curl -s -o /dev/null -w "%{http_code}" "http://target:8080/attachment?id=$i"
   done
   

2. Access a valid attachment – Once a 200 response is found, download it.

   curl -O "http://target:8080/attachment?id=123"
   

3. Execute malicious attachment – If the attachment is executable (e.g., .exe, .sh), the attacker can trigger execution via the application's processing logic.

Note: No public exploit code is available. The above is a conceptual demonstration.

Blue Team (Defensive)

Detection:

• Monitor for sequential or rapid requests to /attachment endpoint.
• Alert on any access to /attachment without prior authentication.
• Use WAF rules to block direct access to attachment endpoints.

Hunting:

• Search logs for patterns like GET /attachment?id= from external IPs.
• Check for unusual file downloads or executions.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /attachment?id=<number> from unknown IPs.
  • Repeated 200 responses to sequential ID requests.
• File System:
  • Unexpected files in /attachments/ directory.
  • New executable files in temporary directories.
• Logs:
  • Web server logs showing GET /attachment?id= without prior session.
  • Application logs showing unauthorized access attempts.

Detection Engineering

YARA Rule

rule CVE_2025_66956_Asseco_SEE_Live_2_0 {
    meta:
        description = "Detects exploitation attempts of CVE-2025-66956 via URL patterns"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-66956"
    strings:
        $url_pattern = "/attachment?id="
        $sequential = /\?id=\d{1,5}/  // Matches numeric IDs
    condition:
        $url_pattern and #sequential > 5  // More than 5 sequential requests
}

Sigma Rule

title: CVE-2025-66956 Exploitation Attempt
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects multiple requests to /attachment endpoint without authentication
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem: '/attachment'
        cs-uri-query|contains: 'id='
    condition: selection
    timeframe: 5m
    condition: selection | count() > 10
falsepositives:
    - Legitimate internal users
level: high

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2025-66956 - Asseco SEE Live 2.0 Insecure Access Control";
    flow:to_server,established;
    content:"GET"; http_method;
    content:"/attachment"; http_uri;
    content:"id="; http_uri;
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate – Place the Asseco SEE Live 2.0 server behind a firewall or VPN, restricting access to trusted IPs only.
2. Disable – If possible, disable the Contact Plan, E-Mail, SMS, and Fax components until a patch is available.
3. Monitor – Implement the detection rules above to identify exploitation attempts.

Long-term:

• Contact Asseco SEE for an official patch or workaround.
• Consider migrating to a different solution if no patch is provided.
• Implement a Web Application Firewall (WAF) with custom rules to block direct access to /attachment endpoints.

Workaround:

• Modify the application's configuration to require authentication for all attachment-related URLs (if possible).

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert