CVE-2026-27774

Executive Summary

CVE-2026-27774 is a local privilege escalation vulnerability in Acronis True Image for Windows, caused by insecure DLL loading (DLL hijacking). An authenticated attacker with local access can exploit this weakness to execute arbitrary code with elevated privileges, potentially leading to full system compromise. The vulnerability affects builds prior to 42902. Acronis has released a patched version, and immediate upgrade is recommended.

Supply Chain & Package Security

This vulnerability is not related to any open-source package manager (NPM, PyPI, Go, Ruby). It affects a proprietary Windows application distributed by Acronis. The supply chain risk is limited to the integrity of the Acronis software distribution channel.

CVSS Breakdown & Threat Level

• CVSS Score: 6.7 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Local (AV:L) – The attacker must have local access to the system.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: Low (PR:L) – The attacker needs a standard user account.
• User Interaction: None (UI:N) – No user action is needed beyond the attacker’s own actions.
• Scope: Unchanged (S:U) – The vulnerability does not cross security boundaries.
• Confidentiality Impact: High (C:H) – Full data access possible.
• Integrity Impact: High (I:H) – Full system modification possible.
• Availability Impact: High (A:H) – Full system denial of service possible.

Threat Level: Medium. While the CVSS score is moderate, the potential for full system compromise makes this a significant risk for any organization using the vulnerable software.

Deep Dive & Mechanics

The vulnerability is a classic DLL hijacking issue (CWE-427). Acronis True Image loads a dynamic-link library (DLL) without specifying a fully qualified path. When the application runs, it searches for the DLL in a specific order, including the current working directory or other user-writable locations. An attacker with local access can place a malicious DLL in one of these search paths. When the application loads the DLL, the malicious code executes within the context of the application, which may run with elevated privileges (e.g., SYSTEM or Administrator).

Attack Flow:

1. Attacker gains local access to a Windows system (e.g., via a compromised user account).
2. Attacker identifies a DLL that Acronis True Image loads unsafely.
3. Attacker places a malicious DLL in a directory that is searched before the legitimate DLL location (e.g., the application’s working directory or a user-writable path).
4. When a privileged user (or a scheduled task) launches Acronis True Image, the malicious DLL is loaded.
5. The malicious code executes with the privileges of the application, allowing the attacker to escalate to SYSTEM or Administrator.

Vulnerable vs. Patched Code

The vulnerable code likely uses a relative path or relies on the system’s DLL search order without using SetDllDirectory or specifying a full path. The patched version (build 42902) likely uses absolute paths or calls SetDllDirectory("") to remove the current directory from the search order.

Vulnerable Code (Conceptual):

// Vulnerable: Loads DLL without full path
HMODULE hMod = LoadLibrary(L"helper.dll");

Patched Code (Conceptual):

// Patched: Uses full path to DLL
HMODULE hMod = LoadLibrary(L"C:\\Program Files\\Acronis\\TrueImage\\helper.dll");

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a Windows system with a vulnerable Acronis True Image build (< 42902).
• A standard user account.

Steps:

1. Identify a DLL loaded by Acronis True Image that is vulnerable to hijacking. Common candidates include version.dll, dbghelp.dll, or custom DLLs.
2. Create a malicious DLL that executes a payload (e.g., add a user to the Administrators group or spawn a reverse shell).
3. Place the malicious DLL in a directory that is searched before the legitimate one (e.g., the application’s install directory or a user-writable path like %TEMP%).
4. Trigger the application launch (e.g., wait for a scheduled task or user action).
5. The malicious DLL executes with elevated privileges.

Example Malicious DLL (C++):

#include <windows.h>

BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) {
    if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
        // Execute command to add user to Administrators group
        system("net localgroup Administrators attacker /add");
    }
    return TRUE;
}

Blue Team

Detection:

• Monitor for unexpected DLL loads in the context of TrueImage.exe or related processes.
• Use Sysmon Event ID 7 (Image loaded) to detect DLLs loaded from unusual paths.
• Look for file creation events in directories like %TEMP% or the application directory that contain DLLs.

Hunting:

• Search for DLLs named after common hijacking targets (e.g., version.dll, dbghelp.dll) in user-writable directories.
• Check for processes running with elevated privileges that have loaded DLLs from non-standard paths.

Prevention:

• Apply the patch (build 42902 or later).
• Use AppLocker or Windows Defender Application Control (WDAC) to block unauthorized DLLs.
• Enable Safe DLL Search Mode (registry key: HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\SafeDllSearchMode).

Indicators of Compromise (IOCs)

• File Hashes (Malicious DLL): (Example – replace with actual if discovered)
  • SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• File Paths:
  • C:\Users\<username>\AppData\Local\Temp\version.dll
  • C:\Program Files\Acronis\TrueImage\version.dll (if overwritten)
• Process Anomalies:
  • TrueImage.exe loading DLLs from %TEMP% or other user-writable paths.
• Registry Changes:
  • Addition of user to Administrators group.
  • New service or scheduled task creation.

Detection Engineering

YARA Rule

rule CVE_2026_27774_DLL_Hijack {
    meta:
        description = "Detects potential DLL hijacking for CVE-2026-27774"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-27774"
    strings:
        $s1 = "TrueImage.exe" nocase
        $s2 = "version.dll" nocase
        $s3 = "dbghelp.dll" nocase
    condition:
        $s1 and ($s2 or $s3)
}

Sigma Rule

title: CVE-2026-27774 - Acronis True Image DLL Hijacking
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects DLL load events from unusual paths for Acronis True Image
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 7
        Image|endswith: '\TrueImage.exe'
        ImageLoaded|contains:
            - '\AppData\Local\Temp\'
            - '\Users\'
    condition: selection
falsepositives:
    - Legitimate DLLs placed in user directories by IT admins
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"CVE-2026-27774 - Acronis True Image DLL Hijack Attempt"; flow:to_server,established; content:"TrueImage.exe"; nocase; content:"version.dll"; nocase; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade to Acronis True Image build 42902 or later. This is the only definitive fix.
2. Workaround: If patching is not immediately possible, restrict local access to the system and monitor for suspicious DLL loads.

Long-Term Mitigations:

• Implement the principle of least privilege (PoLP) for all user accounts.
• Use application whitelisting (e.g., AppLocker) to prevent unauthorized DLLs from executing.
• Enable Safe DLL Search Mode via Group Policy.
• Regularly audit and update all software, especially security-critical applications.

Detection:

• Deploy the provided YARA, Sigma, and Suricata rules to detect exploitation attempts.
• Monitor for unusual file creation in application directories.

Valters IT

{/* [Security Hash: DD4C2DF1C3B653C08DA62601] */}