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CVE-2026-28704
Technical Analysis of the Vulnerability
Emocheck is a lightweight tool created by JPCERT/CC to help Windows users detect infections of the Emotet malware. The vulnerability exists because Emocheck does not properly control the search path when loading required Dynamic Link Libraries (DLLs) – a weakness classified as CWE-427 (Uncontrolled Search Path Element).
When a Windows application needs a DLL, the operating system follows a specific search order: the directory from which the application loaded, the system directory, the Windows directory, and finally directories listed in the `PATH` environment variable. If a developer relies on implicit loading without specifying an absolute or safely‑qualified path, an attacker can place a malicious DLL earlier in the search order.
In Emocheck, the tool was designed to load certain DLLs from the current working directory without any path restriction. Consequently, if a specially crafted DLL is placed in the same folder as the `Emocheck.exe` binary, the application will load and execute that malicious DLL as soon as the user launches the tool.
The attack scenario is straightforward:
- The attacker crafts a malicious DLL that, when loaded, executes arbitrary code.
- They trick the victim into copying (or unknowingly placing) this DLL into the same directory where Emocheck resides.
- When the victim runs Emocheck, the malicious DLL is loaded and executed with the privileges of the invoking user.
Because no authentication or integrity check is performed on the DLL, the attacker can achieve full code execution. The vulnerability affects all versions of Emocheck, and JPCERT/CC has confirmed that the tool is no longer maintained.
CVSS v3.0 metrics: AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H → Base Score 7.8 (High).
CVSS v4.0 metrics: AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H → Base Score 8.4 (High).
DailyCVE Form:
Platform: Windows
Version: all versions
Vulnerability: DLL Hijacking
Severity: High
date: 2026‑04‑10
Prediction: No patch (tool discontinued)
What Undercode Say
Identify the default DLLs loaded by Emocheck (import table) <blockquote> dumpbin /imports emocheck.exe | findstr ".dll" strings emocheck.exe | grep -i ".dll" Monitor DLL load events while Emocheck runs procmon.exe /AcceptEula /Minimized /BackingFile emocheck.pml procmon.exe /OpenLog emocheck.pml /Filter "Process Name eq 'emocheck.exe' and Operation eq 'Load Image'" Generate a benign test DLL (C source for analysis) gcc -shared -o test.dll test.c
// test.c – Minimal DLL to log loading
include <windows.h>
BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {
if (fdwReason == DLL_PROCESS_ATTACH) {
MessageBox(NULL, "DLL loaded!", "Emocheck Test", MB_OK);
// Place actual payload here (e.g., reverse shell, EDR bypass)
}
return TRUE;
}
Exploit
- Prepare the payload – Compile a malicious DLL that executes arbitrary code (e.g., adds an administrator account, launches a reverse shell, or disables security software).
- Place the DLL – Copy the crafted DLL to the same directory where `Emocheck.exe` is stored.
– Example name: `version.dll` (a common placeholder; the actual required DLL name can be obtained from Emocheck’s import table).
3. Wait for user execution – The victim runs Emocheck (double‑clicks or runs from command line).
4. Code execution – Emocheck loads the attacker‑controlled DLL with the victim’s privileges. If the victim has administrative rights, the attacker gains full control of the host.
Protection
- Immediate action – Stop using Emocheck entirely. JPCERT/CC has discontinued the tool because the Emotet threat has subsided.
- Application control – Deploy Windows Defender Application Control (WDAC) or AppLocker to block unsigned/untrusted DLLs from loading.
- Secure DLL search mode – Set the `CWDIllegalInDllSearch` registry key or enable `SetDllDirectory(“”)` in custom applications to remove the current directory from the DLL search order.
- Monitor file system – Use Sysmon (Event ID 7) or EDR solutions to detect creation of DLL files in sensitive directories and to log `Load Image` events.
- User education – Warn users to never download or run Emocheck from untrusted sources and to avoid mixing executable files with untrusted content.
Impact
- Confidentiality – Attackers can read sensitive files, credentials, and emails.
- Integrity – System files, registry keys, and installed software can be modified.
- Availability – Critical services may be disrupted or rendered unusable.
- Privilege escalation – Execution occurs with the victim’s rights; if the victim is a local administrator, the attacker obtains full system control.
- Persistence – Malicious code can be installed to survive reboots.
- Lateral movement – Compromised credentials can be used to move to other machines on the network.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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