CVE-2026-28720

Executive Summary

CVE-2026-28720 is a medium-severity vulnerability in Acronis Cyber Protect 17 (Linux and Windows) that allows an unauthorized attacker to modify settings due to insufficient authorization checks. The vulnerability exists in builds prior to 41186. With a CVSS score of 4.3, it is considered a moderate risk, primarily affecting the integrity of the system configuration. No public proof-of-concept (PoC) or exploit code has been identified at this time. The vendor has released a patched build (41186) to address the issue.

Supply Chain & Package Security

This vulnerability is not related to an open-source package manager (NPM, PyPI, Go, Ruby). It affects a proprietary commercial product, Acronis Cyber Protect 17. Therefore, supply chain security considerations are limited to ensuring that the software is obtained from official Acronis channels and that the update process is verified.

CVSS Breakdown & Threat Level

• CVSS Score: 4.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication is needed.
• User Interaction (UI): None (N) – No user action is required.
• Scope (S): Unchanged (U) – The vulnerable component and the impacted component are the same.
• Confidentiality (C): None (N) – No data is exposed.
• Integrity (I): Low (L) – Unauthorized modification of settings is possible.
• Availability (A): None (N) – No impact on system availability.

Threat Level: Medium. The vulnerability allows for unauthorized configuration changes, which could lead to further compromise or disruption of service. The lack of required privileges and user interaction makes it relatively easy to exploit, but the impact is limited to integrity.

Deep Dive & Mechanics

The vulnerability stems from insufficient authorization checks in the Acronis Cyber Protect 17 management interface. An unauthenticated attacker can send specially crafted network requests to the affected service, bypassing authentication and authorization mechanisms. This allows the attacker to modify system settings without proper credentials.

The root cause is a missing or improperly implemented access control check in the API endpoint responsible for handling configuration changes. The application fails to verify that the requesting user has the necessary permissions before processing the request. This is a classic example of CWE-862: Missing Authorization.

The attack vector is network-based, meaning the attacker does not need local access to the system. The attack complexity is low, as no special conditions or advanced techniques are required. The attacker only needs to know the network address of the vulnerable service.

Vulnerable vs. Patched Code

Since the exact code is proprietary, a generic example of the vulnerability is provided.

Vulnerable Code (Conceptual):

# Vulnerable endpoint - no authorization check
@app.route('/api/settings/update', methods=['POST'])
def update_settings():
    data = request.json
    # Directly apply settings without checking user permissions
    apply_settings(data)
    return jsonify({"status": "success"})

Patched Code (Conceptual):

# Patched endpoint - with authorization check
@app.route('/api/settings/update', methods=['POST'])
def update_settings():
    # Verify user is authenticated and has admin role
    user = get_current_user()
    if not user or not user.has_role('admin'):
        return jsonify({"error": "Unauthorized"}), 403
    data = request.json
    apply_settings(data)
    return jsonify({"status": "success"})

The patched version introduces a check to ensure the user is authenticated and has the appropriate role (e.g., admin) before allowing settings modification.

Exploitation & Lab Setup

Red Team

Objective: Modify system settings without authentication.

Prerequisites:

• A vulnerable instance of Acronis Cyber Protect 17 (build < 41186).
• Network access to the management interface (typically port 443 or 8443).

Steps:

1. Identify the target IP address and port of the Acronis Cyber Protect management interface.
2. Craft a POST request to the vulnerable endpoint (e.g., /api/settings/update).
3. Include the desired configuration changes in the request body (e.g., JSON payload).
4. Send the request without any authentication headers.
5. Verify that the settings have been modified.

Example Request (using curl):

curl -X POST https://target:8443/api/settings/update \
  -H "Content-Type: application/json" \
  -d '{"setting_name": "example_setting", "value": "malicious_value"}'

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

Blue Team

Objective: Detect and prevent exploitation attempts.

Detection:

• Monitor for unauthorized POST requests to /api/settings/update or similar endpoints.
• Look for requests without valid authentication tokens or session cookies.
• Analyze network traffic for unusual patterns or payloads targeting configuration endpoints.

Prevention:

• Apply the vendor patch (build 41186 or later) immediately.
• Implement network segmentation to restrict access to the management interface.
• Use a Web Application Firewall (WAF) to block requests to sensitive endpoints without proper authentication.
• Enable logging and alerting for all configuration changes.

Indicators of Compromise (IOCs)

• Network:

  • POST requests to /api/settings/update without authentication.
  • Unusual configuration change events in logs.
  • Connections from unknown IP addresses to the management interface.

• System:

  • Unexpected changes to system settings (e.g., backup schedules, security policies).
  • New user accounts or modified permissions.
  • Unusual entries in application logs indicating failed authorization attempts.

• File:

  • Modified configuration files (e.g., config.json, settings.xml).
  • Presence of unauthorized scripts or binaries.

Detection Engineering

YARA Rule

rule CVE_2026_28720_Acronis_Settings_Modification {
    meta:
        description = "Detects attempts to exploit CVE-2026-28720 by identifying unauthorized settings modification requests"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-28720"
    strings:
        $s1 = "/api/settings/update" ascii wide nocase
        $s2 = "setting_name" ascii wide nocase
        $s3 = "value" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: Unauthorized Settings Modification Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit CVE-2026-28720 by monitoring for unauthorized POST requests to the settings endpoint
author: Valters IT
date: 2026/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-28720
logsource:
    category: webserver
    product: acronis
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/api/settings/update'
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate administrative actions
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-28720 - Unauthorized Settings Modification Attempt"; flow:to_server; content:"POST"; http_method; content:"/api/settings/update"; http_uri; content:"setting_name"; http_client_body; content:"value"; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade Acronis Cyber Protect 17 to build 41186 or later. This is the primary fix.
2. Network Access Control: Restrict access to the management interface to trusted IP addresses only.
3. Monitor Logs: Review application and system logs for any signs of unauthorized access or configuration changes.

Long-Term Measures:

1. Principle of Least Privilege: Ensure that all API endpoints enforce proper authorization checks.
2. Regular Security Audits: Conduct periodic code reviews and penetration testing.
3. Web Application Firewall (WAF): Deploy a WAF to block malicious requests.
4. Vulnerability Management: Subscribe to vendor security advisories and apply patches promptly.

Workaround (if patching is not immediately possible):

• Disable remote access to the management interface if not required.
• Implement a reverse proxy with authentication to add an additional layer of security.

Valters IT
Securing Digital Frontiers