1 files changed, 43 insertions, 0 deletions
diff --git a/windows/utils/dll_hijacking_protection.c b/windows/utils/dll_hijacking_protection.c
new file mode 100644
index 00000000..fe9ae59c
--- /dev/null
+++ b/windows/utils/dll_hijacking_protection.c
@@ -0,0 +1,43 @@
+/*
+ * If the OS provides it, call SetDefaultDllDirectories() to prevent
+ * DLLs from being loaded from the directory containing our own
+ * binary, and instead only load from system32.
+ *
+ * This is a protection against hijacking attacks, if someone runs
+ * PuTTY directly from their web browser's download directory having
+ * previously been enticed into clicking on an unwise link that
+ * downloaded a malicious DLL to the same directory under one of
+ * various magic names that seem to be things that standard Windows
+ * DLLs delegate to.
+ *
+ * It shouldn't break deliberate loading of user-provided DLLs such as
+ * GSSAPI providers, because those are specified by their full
+ * pathname by the user-provided configuration.
+ */
+
+#include "putty.h"
+
+void dll_hijacking_protection(void)
+{
+    static HMODULE kernel32_module;
+    DECL_WINDOWS_FUNCTION(static, BOOL, SetDefaultDllDirectories, (DWORD));
+
+    if (!kernel32_module) {
+        kernel32_module = load_system32_dll("kernel32.dll");
+#if !HAVE_SETDEFAULTDLLDIRECTORIES
+        /* For older Visual Studio, this function isn't available in
+         * the header files to type-check */
+        GET_WINDOWS_FUNCTION_NO_TYPECHECK(
+            kernel32_module, SetDefaultDllDirectories);
+#else
+        GET_WINDOWS_FUNCTION(kernel32_module, SetDefaultDllDirectories);
+#endif
+    }
+
+    if (p_SetDefaultDllDirectories) {
+        /* LOAD_LIBRARY_SEARCH_SYSTEM32 and explicitly specified
+         * directories only */
+        p_SetDefaultDllDirectories(LOAD_LIBRARY_SEARCH_SYSTEM32 |
+                                   LOAD_LIBRARY_SEARCH_USER_DIRS);
+    }
+}