diff --git a/programs/wusa/Makefile.in b/programs/wusa/Makefile.in
index 3042e86bf85..5e60bdf1b06 100644
--- a/programs/wusa/Makefile.in
+++ b/programs/wusa/Makefile.in
@@ -1,4 +1,5 @@
 MODULE    = wusa.exe
+IMPORTS   = cabinet shlwapi
 
 EXTRADLLFLAGS = -mconsole -municode -mno-cygwin
 
diff --git a/programs/wusa/main.c b/programs/wusa/main.c
index c3e3dfd38ce..a719eefc5b7 100644
--- a/programs/wusa/main.c
+++ b/programs/wusa/main.c
@@ -1,5 +1,7 @@
 /*
  * Copyright 2012 Austin English
+ * Copyright 2015 Michael Müller
+ * Copyright 2015 Sebastian Lackner
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -16,18 +18,375 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  */
 
+#include <windows.h>
+#include <fcntl.h>
+#include <fdi.h>
+#include <shlwapi.h>
+
 #include "wine/debug.h"
+#include "wine/list.h"
+#include "wusa.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(wusa);
 
-int __cdecl wmain(int argc, WCHAR *argv[])
+struct installer_tempdir
 {
-    int i;
+    struct list entry;
+    WCHAR *path;
+};
 
-    WINE_FIXME("stub:");
-    for (i = 0; i < argc; i++)
-        WINE_FIXME(" %s", wine_dbgstr_w(argv[i]));
-    WINE_FIXME("\n");
+struct installer_state
+{
+    BOOL norestart;
+    BOOL quiet;
+    struct list tempdirs;
+};
+
+static void * CDECL cabinet_alloc(ULONG cb)
+{
+    return heap_alloc(cb);
+}
+
+static void CDECL cabinet_free(void *pv)
+{
+    heap_free(pv);
+}
+
+static INT_PTR CDECL cabinet_open(char *pszFile, int oflag, int pmode)
+{
+    DWORD dwAccess = 0;
+    DWORD dwShareMode = 0;
+    DWORD dwCreateDisposition = OPEN_EXISTING;
+
+    switch (oflag & _O_ACCMODE)
+    {
+    case _O_RDONLY:
+        dwAccess = GENERIC_READ;
+        dwShareMode = FILE_SHARE_READ | FILE_SHARE_DELETE;
+        break;
+    case _O_WRONLY:
+        dwAccess = GENERIC_WRITE;
+        dwShareMode = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
+        break;
+    case _O_RDWR:
+        dwAccess = GENERIC_READ | GENERIC_WRITE;
+        dwShareMode = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
+        break;
+    }
+
+    if ((oflag & (_O_CREAT | _O_EXCL)) == (_O_CREAT | _O_EXCL))
+        dwCreateDisposition = CREATE_NEW;
+    else if (oflag & _O_CREAT)
+        dwCreateDisposition = CREATE_ALWAYS;
+
+    return (INT_PTR)CreateFileA(pszFile, dwAccess, dwShareMode, NULL, dwCreateDisposition, 0, NULL);
+}
+
+static UINT CDECL cabinet_read(INT_PTR hf, void *pv, UINT cb)
+{
+    HANDLE handle = (HANDLE)hf;
+    DWORD read;
+
+    if (ReadFile(handle, pv, cb, &read, NULL))
+        return read;
 
     return 0;
 }
+
+static UINT CDECL cabinet_write(INT_PTR hf, void *pv, UINT cb)
+{
+    HANDLE handle = (HANDLE)hf;
+    DWORD written;
+
+    if (WriteFile(handle, pv, cb, &written, NULL))
+        return written;
+
+    return 0;
+}
+
+static int CDECL cabinet_close(INT_PTR hf)
+{
+    HANDLE handle = (HANDLE)hf;
+    return CloseHandle(handle) ? 0 : -1;
+}
+
+static LONG CDECL cabinet_seek(INT_PTR hf, LONG dist, int seektype)
+{
+    HANDLE handle = (HANDLE)hf;
+    /* flags are compatible and so are passed straight through */
+    return SetFilePointer(handle, dist, NULL, seektype);
+}
+
+static WCHAR *path_combine(const WCHAR *path, const WCHAR *filename)
+{
+    WCHAR *result;
+    DWORD length;
+
+    if (!path || !filename) return NULL;
+    length = lstrlenW(path) + lstrlenW(filename) + 2;
+    if (!(result = heap_alloc(length * sizeof(WCHAR)))) return NULL;
+
+    lstrcpyW(result, path);
+    if (result[0] && result[lstrlenW(result) - 1] != '\\') lstrcatW(result, L"\\");
+    lstrcatW(result, filename);
+    return result;
+}
+
+static WCHAR *get_uncompressed_path(PFDINOTIFICATION pfdin)
+{
+    WCHAR *file = strdupAtoW(pfdin->psz1);
+    WCHAR *path = path_combine(pfdin->pv, file);
+    heap_free(file);
+    return path;
+}
+
+static BOOL is_directory(const WCHAR *path)
+{
+    DWORD attrs = GetFileAttributesW(path);
+    if (attrs == INVALID_FILE_ATTRIBUTES) return FALSE;
+    return (attrs & FILE_ATTRIBUTE_DIRECTORY) != 0;
+}
+
+static BOOL create_directory(const WCHAR *path)
+{
+    if (is_directory(path)) return TRUE;
+    if (CreateDirectoryW(path, NULL)) return TRUE;
+    return (GetLastError() == ERROR_ALREADY_EXISTS);
+}
+
+static BOOL create_parent_directory(const WCHAR *filename)
+{
+    WCHAR *p, *path = strdupW(filename);
+    BOOL ret = FALSE;
+
+    if (!path) return FALSE;
+    if (!PathRemoveFileSpecW(path)) goto done;
+    if (is_directory(path))
+    {
+        ret = TRUE;
+        goto done;
+    }
+
+    for (p = path; *p; p++)
+    {
+        if (*p != '\\') continue;
+        *p = 0;
+        if (!create_directory(path)) goto done;
+        *p = '\\';
+    }
+    ret = create_directory(path);
+
+done:
+    heap_free(path);
+    return ret;
+}
+
+static INT_PTR cabinet_copy_file(FDINOTIFICATIONTYPE fdint, PFDINOTIFICATION pfdin)
+{
+    HANDLE handle = INVALID_HANDLE_VALUE;
+    WCHAR *file;
+    DWORD attrs;
+
+    if (!(file = get_uncompressed_path(pfdin)))
+        return -1;
+
+    TRACE("Extracting %s -> %s\n", debugstr_a(pfdin->psz1), debugstr_w(file));
+
+    if (create_parent_directory(file))
+    {
+        attrs = pfdin->attribs;
+        if (!attrs) attrs = FILE_ATTRIBUTE_NORMAL;
+        handle = CreateFileW(file, GENERIC_READ | GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, attrs, NULL);
+    }
+
+    heap_free(file);
+    return (handle != INVALID_HANDLE_VALUE) ? (INT_PTR)handle : -1;
+}
+
+static INT_PTR cabinet_close_file_info(FDINOTIFICATIONTYPE fdint, PFDINOTIFICATION pfdin)
+{
+    HANDLE handle = (HANDLE)pfdin->hf;
+    CloseHandle(handle);
+    return 1;
+}
+
+static INT_PTR CDECL cabinet_notify(FDINOTIFICATIONTYPE fdint, PFDINOTIFICATION pfdin)
+{
+    switch (fdint)
+    {
+    case fdintPARTIAL_FILE:
+        FIXME("fdintPARTIAL_FILE not implemented\n");
+        return 0;
+
+    case fdintNEXT_CABINET:
+        FIXME("fdintNEXT_CABINET not implemented\n");
+        return 0;
+
+    case fdintCOPY_FILE:
+        return cabinet_copy_file(fdint, pfdin);
+
+    case fdintCLOSE_FILE_INFO:
+        return cabinet_close_file_info(fdint, pfdin);
+
+    default:
+        return 0;
+    }
+}
+
+static BOOL extract_cabinet(const WCHAR *filename, const WCHAR *destination)
+{
+    char *filenameA = NULL;
+    BOOL ret = FALSE;
+    HFDI hfdi;
+    ERF erf;
+
+    hfdi = FDICreate(cabinet_alloc, cabinet_free, cabinet_open, cabinet_read,
+                     cabinet_write, cabinet_close, cabinet_seek, 0, &erf);
+    if (!hfdi) return FALSE;
+
+    if ((filenameA = strdupWtoA(filename)))
+    {
+        ret = FDICopy(hfdi, filenameA, NULL, 0, cabinet_notify, NULL, (void *)destination);
+        heap_free(filenameA);
+    }
+
+    FDIDestroy(hfdi);
+    return ret;
+}
+
+static const WCHAR *create_temp_directory(struct installer_state *state)
+{
+    static UINT id;
+    struct installer_tempdir *entry;
+    WCHAR tmp[MAX_PATH];
+
+    if (!GetTempPathW(ARRAY_SIZE(tmp), tmp)) return NULL;
+    if (!(entry = heap_alloc(sizeof(*entry)))) return NULL;
+    if (!(entry->path = heap_alloc((MAX_PATH + 20) * sizeof(WCHAR))))
+    {
+        heap_free(entry);
+        return NULL;
+    }
+    for (;;)
+    {
+        if (!GetTempFileNameW(tmp, L"msu", ++id, entry->path))
+        {
+            heap_free(entry->path);
+            heap_free(entry);
+            return NULL;
+        }
+        if (CreateDirectoryW(entry->path, NULL)) break;
+    }
+
+    list_add_tail(&state->tempdirs, &entry->entry);
+    return entry->path;
+}
+
+static BOOL delete_directory(const WCHAR *path)
+{
+    WIN32_FIND_DATAW data;
+    WCHAR *full_path;
+    HANDLE search;
+
+    if (!(full_path = path_combine(path, L"*"))) return FALSE;
+    search = FindFirstFileW(full_path, &data);
+    heap_free(full_path);
+
+    if (search != INVALID_HANDLE_VALUE)
+    {
+        do
+        {
+            if (!wcscmp(data.cFileName, L".")) continue;
+            if (!wcscmp(data.cFileName, L"..")) continue;
+            if (!(full_path = path_combine(path, data.cFileName))) continue;
+            if (data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)
+                delete_directory(full_path);
+            else
+                DeleteFileW(full_path);
+            heap_free(full_path);
+        }
+        while (FindNextFileW(search, &data));
+        FindClose(search);
+    }
+
+    return RemoveDirectoryW(path);
+}
+
+static void installer_cleanup(struct installer_state *state)
+{
+    struct installer_tempdir *tempdir, *tempdir2;
+
+    LIST_FOR_EACH_ENTRY_SAFE(tempdir, tempdir2, &state->tempdirs, struct installer_tempdir, entry)
+    {
+        list_remove(&tempdir->entry);
+        delete_directory(tempdir->path);
+        heap_free(tempdir->path);
+        heap_free(tempdir);
+    }
+}
+
+static BOOL install_msu(const WCHAR *filename, struct installer_state *state)
+{
+    const WCHAR *temp_path;
+    BOOL ret = FALSE;
+
+    list_init(&state->tempdirs);
+
+    TRACE("Processing msu file %s\n", debugstr_w(filename));
+
+    if (!(temp_path = create_temp_directory(state))) return FALSE;
+    if (!extract_cabinet(filename, temp_path))
+    {
+        ERR("Failed to extract %s\n", debugstr_w(filename));
+        goto done;
+    }
+
+    ret = TRUE;
+
+done:
+    installer_cleanup(state);
+    return ret;
+}
+
+int __cdecl wmain(int argc, WCHAR *argv[])
+{
+    struct installer_state state;
+    const WCHAR *filename = NULL;
+    int i;
+
+    state.norestart = FALSE;
+    state.quiet = FALSE;
+
+    if (TRACE_ON(wusa))
+    {
+        TRACE("Command line:");
+        for (i = 0; i < argc; i++)
+            TRACE(" %s", wine_dbgstr_w(argv[i]));
+        TRACE("\n");
+    }
+
+    for (i = 1; i < argc; i++)
+    {
+        if (argv[i][0] == '/')
+        {
+            if (!wcscmp(argv[i], L"/norestart"))
+                state.norestart = TRUE;
+            else if (!wcscmp(argv[i], L"/quiet"))
+                state.quiet = TRUE;
+            else
+                FIXME("Unknown option: %s\n", wine_dbgstr_w(argv[i]));
+        }
+        else if (!filename)
+            filename = argv[i];
+        else
+            FIXME("Unknown option: %s\n", wine_dbgstr_w(argv[i]));
+    }
+
+    if (!filename)
+    {
+        FIXME("Missing filename argument\n");
+        return 1;
+    }
+
+    return !install_msu(filename, &state);
+}
diff --git a/programs/wusa/wusa.h b/programs/wusa/wusa.h
new file mode 100644
index 00000000000..c6bf7eda11e
--- /dev/null
+++ b/programs/wusa/wusa.h
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2015 Michael Müller
+ * Copyright 2015 Sebastian Lackner
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+static void *heap_alloc(size_t len) __WINE_ALLOC_SIZE(1);
+static inline void *heap_alloc(size_t len)
+{
+    return HeapAlloc(GetProcessHeap(), 0, len);
+}
+
+static inline BOOL heap_free(void *mem)
+{
+    return HeapFree(GetProcessHeap(), 0, mem);
+}
+
+static inline char *strdupWtoA(const WCHAR *str)
+{
+    char *ret = NULL;
+    DWORD len;
+
+    if (!str) return ret;
+    len = WideCharToMultiByte(CP_ACP, 0, str, -1, NULL, 0, NULL, NULL);
+    if ((ret = heap_alloc(len)))
+        WideCharToMultiByte(CP_ACP, 0, str, -1, ret, len, NULL, NULL);
+    return ret;
+}
+
+static inline WCHAR *strdupAtoW(const char *str)
+{
+    WCHAR *ret = NULL;
+    DWORD len;
+
+    if (!str) return ret;
+    len = MultiByteToWideChar(CP_ACP, 0, str, -1, NULL, 0);
+    if ((ret = heap_alloc(len * sizeof(WCHAR))))
+        MultiByteToWideChar(CP_ACP, 0, str, -1, ret, len);
+    return ret;
+}
+
+static inline WCHAR *strdupW(const WCHAR *str)
+{
+    WCHAR *ret;
+    if (!str) return NULL;
+    ret = heap_alloc((lstrlenW(str) + 1) * sizeof(WCHAR));
+    if (ret) lstrcpyW(ret, str);
+    return ret;
+}