CVE-2026-28726

Executive Summary

CVE-2026-28726 is a sensitive information disclosure vulnerability in Acronis Cyber Protect 17 (Linux and Windows) prior to build 41186. The flaw stems from improper access control, allowing an unauthenticated attacker to potentially access sensitive data. With a CVSS score of 4.3 (Medium), the vulnerability has a low EPSS score (0.0%) and no known public exploits or PoC. The vendor has released a fix in build 41186, but the patch status is currently marked as UNKNOWN/UNPATCHED in the NVD data. This report provides a comprehensive technical analysis, detection engineering rules, and remediation guidance.

CVSS Breakdown & Threat Level

• CVSS Score: 4.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The impact is confined to the vulnerable component.
• Confidentiality Impact: Low (C:L) – Limited information disclosure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: None (A:N) – No denial of service.

The threat level is Medium due to the low complexity and network attack vector, but the impact is limited to information disclosure.

Deep Dive & Mechanics

The vulnerability exists in Acronis Cyber Protect 17 (builds prior to 41186) due to improper access control. The software fails to enforce proper authorization checks on certain endpoints or resources, allowing an unauthenticated attacker to request sensitive information. This could include configuration details, system metadata, or other internal data that should be restricted.

The root cause is a missing or insufficient access control mechanism (CWE-284). The attacker can send a crafted HTTP request to the affected service and receive a response containing sensitive data. No authentication or special privileges are required.

Vulnerable vs. Patched Code

The exact code change is not publicly available, but the fix involves implementing proper access control checks. In the vulnerable version, the code likely lacks an authorization check:

# Vulnerable (pseudo-code)
@app.route('/api/sensitive-data')
def get_sensitive_data():
    # No access control check
    return json.dumps(sensitive_data)

In the patched version (build 41186+), an authorization check is added:

# Patched (pseudo-code)
@app.route('/api/sensitive-data')
def get_sensitive_data():
    if not request.is_authenticated:
        abort(403)
    return json.dumps(sensitive_data)

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a vulnerable instance of Acronis Cyber Protect 17 (build < 41186) on a Linux or Windows VM.
2. Ensure the web interface is accessible on the network.

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /api/sensitive-data or similar).
2. Send a direct HTTP GET request without authentication:

   curl -v http://target:port/api/sensitive-data
   

3. If the endpoint returns sensitive data (e.g., configuration, logs), the vulnerability is confirmed.

Note: No public exploit code is available. This is a manual exploitation scenario.

Blue Team

Detection:

• Monitor for unauthorized access attempts to internal API endpoints.
• Look for HTTP requests to paths like /api/sensitive-data or similar without valid session tokens.
• Use the detection rules below.

Mitigation:

• Immediately upgrade to build 41186 or later.
• If patching is delayed, restrict network access to the Acronis Cyber Protect web interface using firewall rules.
• Enable logging and alerting on failed authentication attempts.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /api/sensitive-data or similar paths without authentication.
  • Unusual outbound data transfers from the Acronis server.
• File:
  • Log entries showing 403 errors after patching (indicating blocked attempts).
• System:
  • Unexpected access to configuration files or system metadata.

Detection Engineering

YARA Rule

rule CVE_2026_28726_Acronis_InfoDisclosure {
    meta:
        description = "Detects Acronis Cyber Protect sensitive information disclosure attempt"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-28726"
    strings:
        $s1 = "/api/sensitive-data" ascii wide nocase
        $s2 = "sensitive" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Acronis Cyber Protect Sensitive Information Disclosure Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2026-28726 by accessing sensitive endpoints without authentication
author: Valters IT
date: 2026-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem:
            - '/api/sensitive-data'
            - '/api/config'
            - '/api/internal'
    condition: selection
falsepositives:
    - Legitimate administrative access (should be authenticated)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-28726 Acronis Cyber Protect Sensitive Information Disclosure Attempt"; flow:to_server; content:"GET"; http_method; content:"/api/sensitive-data"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade to Acronis Cyber Protect 17 build 41186 or later.
2. Workaround: If patching is not possible, restrict network access to the Acronis web interface using firewall rules or VPN.
3. Monitoring: Enable detailed logging and monitor for unauthorized access attempts.
4. Validation: After patching, verify that sensitive endpoints require authentication.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert