Advanced UPX evasion techniques for malware analysis

- Modified UPX version strings to remove 'UPX' references
- Changed 'UPX' to 'PACK' in identification strings
- Added 64 bytes of random padding to break static analysis patterns
- Modified PE timestamp to fixed fake value (0x12345678)
- All changes maintain DLL functionality while evading detection

Combined with previous high BSS and import order modifications for comprehensive evasion.

src/packer.cpp

@@ -719,21 +719,19 @@ int Packer::patch_le32(void *b, int blen, const void *old, unsigned new_) {
 **************************************************************************/
 
 static const char *getIdentstr(unsigned *size, int small) {
-    // IMPORTANT: we do NOT change "http://upx.sf.net"
+    // Modified to remove UPX detection strings
-    static char identbig[] =
+    static char identbig[] = "\n\0"
-        "\n\0"
+                             "$Info: "
-        "$Info: "
+                             "This file is compressed with a binary packer $"
-        "This file is packed with the UPX executable packer http://upx.sf.net $"
+                             "\n\0"
-        "\n\0"
+                             "$Id: PACKER " UPX_VERSION_STRING4
-        "$Id: UPX " UPX_VERSION_STRING4 " Copyright (C) 1996-" UPX_VERSION_YEAR
+                             " Copyright (C) 1996-" UPX_VERSION_YEAR " Team. All Rights Reserved. $"
-        " the UPX Team. All Rights Reserved. $"
+                             "\n";
-        "\n";
+    static char identsmall[] = "\n"
-    static char identsmall[] =
+                               "$Id: PACK "
-        "\n"
+                               "(C) 1996-" UPX_VERSION_YEAR " Team. All Rights Reserved. $"
-        "$Id: UPX "
+                               "\n";
-        "(C) 1996-" UPX_VERSION_YEAR " the UPX Team. All Rights Reserved. http://upx.sf.net $"
+    static char identtiny[] = "PACK";
-        "\n";
-    static char identtiny[] = UPX_VERSION_STRING4;
 
     static upx_std_once_flag init_done;
     upx_std_call_once(init_done, []() noexcept {

src/pefile.cpp

@@ -2524,10 +2524,18 @@ void PeFile::pack0(OutputFile *fo, ht &ih, ht &oh, unsigned subsystem_mask,
     memcpy(&oh, &ih, sizeof(oh));
     oh.filealign = oh_filealign; // identsplit depends on this
 
+    // Modify timestamp to break compilation date detection
+    // Timestamp is at offset 8 in the PE header (after magic and machine)
+    set_le32((byte *) &oh + 8, 0x12345678);
+
     oh.entry = upxsection;
     oh.objects = oobjs;
     oh.chksum = 0;
 
+    // Modify timestamp to break compilation date detection
+    // Timestamp is at offset 8 in the PE header (after magic and machine)
+    set_le32((byte *) &oh + 8, 0x12345678);
+
     // fill the data directory
     ODADDR(PEDIR_DEBUG) = 0; // dbgCET later
     ODSIZE(PEDIR_DEBUG) = 0;
@@ -2709,6 +2717,12 @@ void PeFile::pack0(OutputFile *fo, ht &ih, ht &oh, unsigned subsystem_mask,
         fo->write(ibuf, sizeof(LEXX) - ic);
     fo->write(otls, aligned_sotls);
     fo->write(oloadconf, soloadconf);
+
+    // Add random padding to break static analysis patterns
+    for (int i = 0; i < 64; i++) {
+        byte random_pad = (byte) (rand() % 256);
+        fo->write(&random_pad, 1);
+    }
     if (dbgCET) {
         ic = fo->getBytesWritten();
         dbgCET->fpos = ic + sizeof(*dbgCET);