Yara WorkBench

Author: David Zimmer
Date: 12.17.19 - 2:56am

Releasing a new tool today to help you develop and test Yara Signatures.

Yara Workbench is a full IDE with syntax highlighting, code completion, bench marking, match offsets, and in depth match details.

Since the initial video I had added in a couple more bonuses such as:
  • module dump: (yara -D option)
    • loads into a syntax highlight control
    • if intVal > 9 dump values default to hex
    • dll_imports[]{.name, .funcCount} fields
  • launch selected file in an internal or external hex editor
  • launch selected file in external disassembler

I also added two new functions to the pe module. pe.dbg(string) and pe.dbg(int). These can be used as a simple way to get some insight into how yara is running.

This can come in handy for example in the following scenario:
  • pe.imphash() output is not included in the pe module dump
  • a sample file has a corrupt import table
  • what value does imphash() return? hint its not UNDEFINED or ""
With the new functions we can display its output with pe.dbg(pe.imphash()) to see the value of d41d8cd98f00b204e9800998ecf8427e which is md5("")

This could also be useful if a uint32() read was not returning what you expected, and wanted an easy way to see some debug output.

The dbg function will always return 1 so it can be used in the condition section without error.

Another useful example would be using it to get yara to dump pe section entropy:

import "pe"
import "math"

rule test
        for all i in (0 .. pe.number_of_sections -1):(


Another example to see how yara handles corrupt import tables or resources:

rule dumpImportState
            pe.dbg("imphash", pe.imphash()) and
            pe.dbg("import_errors", pe.import_errors) and
            pe.dbg("NumImports" , pe.number_of_imports-1) and 
            for all i in (0 .. pe.number_of_imports):(
                pe.dbg( pe.dll_imports[i].funcCount, pe.dll_imports[i].name) 

rule dumpResources
            pe.dbg("NumResources" , pe.number_of_resources-1) and 
            for any i in (0 .. pe.number_of_resources-1):(
                not pe.dbgw(pe.resources[i].name_string) 

I hacked it into an existing module since the built in functions like uint32() get compiled into rules as binary opcodes and it just wasnt worth the fuss to add a native dbg() function at this point. Adding new functions to modules was quite easy below are the basic mods I used. (More details on the import_errors and dll_imports[] can be found in Yara git issue 1224)



  declare_function("dbgw", "s", "i", dbgw); //wide string version for resource names
  declare_function("dbg", "s", "i", dbg);   //name,arg,retType,func
  declare_function("dbg", "i", "i", dbgi);
  declare_function("dbg", "f", "i", dbgf);
  declare_function("dbg", "sf", "i", dbgsf);
  declare_function("dbg", "si", "i", dbgsi);
  declare_function("dbg", "is", "i", dbgis);
  declare_function("dbg", "ii", "i", dbgii);
  declare_function("dbg", "ss", "i", dbgss);

  declare_function("isdef", "s", "i", isdef);

define_function(dbgw) { char buf[255] = { 0 }; int i = 0, j = 0; char* name = string_argument(1); while (i < 253) { if (name[i] == 0 && name[i + 1] == 0) break; if (name[i] != 0) { buf[j++] = name[i]; } i++; } vb_dbg(cb_dbg, buf); return_integer(1); } define_function(dbg) { char* name = string_argument(1); vb_dbg(cb_dbg, name); return_integer(1); } define_function(dbgii) { char buf[255] = { 0 }; int v = integer_argument(1); int z = integer_argument(2); snprintf(buf, sizeof(buf)-1, "0x%x 0x%x", v,z); vb_dbg(cb_dbg, buf); return_integer(1); } define_function(dbgss) { char buf[255] = { 0 }; char* v = string_argument(1); char* z = string_argument(2); snprintf(buf, sizeof(buf)-1, "%s %s", v, z); vb_dbg(cb_dbg, buf); return_integer(1); } define_function(dbgi) { char buf[255] = { 0 }; int v = integer_argument(1); if (v < 10) snprintf(buf, sizeof(buf)-1, "%d", v); else snprintf(buf, sizeof(buf)-1, "0x%x", v); vb_dbg(cb_dbg, buf); return_integer(1); } define_function(dbgf) { char buf[255] = {0}; float v = float_argument(1); snprintf(buf, sizeof(buf)-1, "%.6f", v); vb_dbg(cb_dbg, buf); return_integer(1); } define_function(dbgsf) { char* txt = string_argument(1); float v = float_argument(2); int sz = strlen(txt) + 255; char* buf = (char*)malloc(sz); if (buf == NULL) { vb_dbg(cb_dbg, "dbgsf Failed to malloc %d bytes",sz); return_integer(1); } snprintf(buf, sz-1, "%s = %.6f", txt, v); vb_dbg(cb_dbg, buf); free(buf); return_integer(1); } define_function(dbgis) { char* txt = string_argument(2); int v = integer_argument(1); int sz = strlen(txt) + 255; char* buf = (char*)malloc(sz); if (buf == NULL) { vb_dbg(cb_dbg, "dbgsi Failed to malloc %d bytes", sz); return_integer(1); } snprintf(buf, sz-1, "0x%x = %s", v, txt); vb_dbg(cb_dbg, buf); free(buf); return_integer(1); } define_function(dbgsi) { char* txt = string_argument(1); int v = integer_argument(2); int sz = strlen(txt) + 255; char* buf = (char*)malloc(sz); if (buf == NULL) { vb_dbg(cb_dbg, "dbgsi Failed to malloc %d bytes", sz); return_integer(1); } snprintf(buf, sz-1, "%s = 0x%x", txt, v); vb_dbg(cb_dbg, buf); free(buf); return_integer(1); } //declare_function("isdef", "s", "i", isdef); //ex: pe.dbg(pe.isdef("rich_signature.offset")) // pe.dbg(pe.isdef("number_of_signatures")) define_function(isdef) { YR_OBJECT* module = module(); char* txt = string_argument(1); if (yr_object_has_undefined_value(module, txt)){ return_integer(0); }else{ return_integer(1); } }

Another one i found I wanted:

declare_function("section_exists", "s", "i", section_name_exists);

	YR_OBJECT* module = module();

	char* name = string_argument(1);

	int64_t n = get_integer(module, "number_of_sections");
	int i;

	if (is_undefined(module, "number_of_sections"))

	for (i = 0; i < yr_min(n, MAX_PE_SECTIONS); i++)
		SIZED_STRING* sect = get_string(module, "sections[%i].name", i);

		if (sect != NULL && strcmp(name, sect->c_string) == 0)


Comments: (0)

Leave Comment:
Email: (not shown)
Message: (Required)
Math Question: 89 + 23 = ? followed by the letter: M 

About Me
More Blogs
Main Site
Posts: (year)
2021 (1)
     VB App object
2020 (8)
     AutoIT versions
     IDA JScript 2
     Using VB6 Obj files from C
     Vb6 PCode Internals
     Vb6 Runtime ForLoop Disasm
     VB6 Pcode - For Loops
     Yara Corrupt Imports
     Yara Undefined values
2019 (12)
     Yara WorkBench
     vbdec dbg updates
     vb6 PCode NOP
     vb6 API and call backs
     how pcode works Pt1
     Reversing PCode Args
     VB6 PCode Disassembly
     VB6 PCode Debugger
     UConnect Disable Cell Modem
2017 (5)
     IDA python over IPC
     dns wildcard blocking
     64bit IDA Plugins
     anterior lines
     misc news/updates
2016 (4)
     KANAL Mod
     Decoders again
     CDO.Message Breakpoints
     SysAnalyzer Updates
2015 (6)
     SysAnalyzer and Site Updates
     crazy decoder
     ida js w/dbg
     flash patching #2
     JS Graphing
     packet reassembly
2014 (5)
     Delphi IDA Plugin
     scdbg IDA integration
     API Hash Database
     Winmerge plugin
     IDACompare Updates
2013 (9)
     Guest Post @ hexblog
     TCP Stream Reassembly
     SysAnalyzer Updates
     Apilogger Video
     Shellcode2Exe trainer
     scdbg updates
     IDA Javascript w/IDE
     Rop Analysis II
     scdbg vrs ROP
2012 (13)
     flash patching
     x64 Hooks
     micro hook
     jmp api+5 *2
     SysAnalyzer Updates
     InjDll runtime config
     C# Asm/Dsm Library
     Shellcode Hook Detection
     Updates II
     Java Hacking
     Windows 8
     Win7 x64
2011 (19)
     Graphing ideas
     .Net Hacking
     Old iDefense Releases
     hll shellcode
     ActionScript Tips
     -patch fu
     scdbg ordinal lookup
     scdbg -api mode
     Peb Module Lists
     scdbg vrs Process Injection
     GetProcAddress Scanner
     scdbg fopen mode
     scdbg findsc mode
     scdbg MemMonitor
     demo shellcodes
     scdbg download
     api hashs redux
     Api hash gen
2010 (11)
     Retro XSS Chat Codes
     Exe as DLL
     Olly Plugins
     Debugging Explorer
     Attach to hidden process
     JS Refactoring
     Asm and Shellcode in CSharp
     Fancy Return Address
     PDF Stream Dumper
     Malcode Call API by Hash
     WinDbg Cheat Sheet
2009 (1)
     GPG Automation