redress

Redress - A tool for analyzing stripped binaries

The redress software is a tool for analyzing stripped Go binaries compiled with the Go compiler. It extracts data from the binary and uses it to reconstruct symbols and performs analysis. It essentially tries to "re-dress" a "stripped" binary. It can be downloaded from its GitHub page.

It has two operation modes. The first is a standalone mode where the binary is executed on its own. The second mode is used when the binary is executed from within radare2 via r2pipe. The binary is aware of its environment and behaves accordingly.

For the examples shown the malware pplauncher (f94ca9b1b01a7b06f19afaac3fbe0a43075c775a) will be used. The malware was first reported by Malwarebytes.

Running it standalone

To run redress, just execute it on the command line. Below are some of the possible flags that can be given. It is possible to use multiple flags to extract different data. If no flags are given, no data is extracted. The idea is to print more information than what is asked by the user.

…

Information

Information about Go binary is shown by using the info command. Information displayed include the compiler version and the date it was released, the build id, GoRoot, and the folder path for the main package.

% redress info pplauncher      
OS         macOS
Arch       amd64
Compiler   1.10 (2018-02-16)
Build ID   3xkvDz8awVOl0TA6jJs9/tcgWkdP85A-MJ6hpnmKm/_xkzRloiGp8H5mHsQgkh/7Kj4aF9BTT0MY_gaQnQI
GoRoot     /usr/local/Cellar/go/1.10/libexec
Main root  /Users/ronald/git/go-workspace/src/keybase.io/safetycrew/pplauncher
# main     1
# std      35
# vendor   2

Packages

The different Go packages used in the binary can be extracted with the packages command. Redress tries to only print the packages that are part of the project and skips standard library and 3rd party library packages.

% redress packages pplauncher 
Packages:
Name  Version
----  -------
main  

Sometimes though, redress fails to classify a package. In this case, the unclassified packages can be printed by also provide the --unknown flag:

% redress packages pplauncher --unknown
Packages:
Name  Version
----  -------
main  

Unknown Packages:
Name  Version
----  -------

To also include the standard library, use the --std flag. For 3rd party packages, use the flag --vendor.

…

The folder locations can be included in the output by using the --filepath flag.

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Extracting types

Redress has multiple commands that can be used to extract different type data. Interfaces can be extracted with the interface command. By default, standard library and vendor interfaces are filtered out. These can be included by also providing the --std and --vendor flag.

% redress types interface pplauncher  
type error interface {
	Error() string
}
type interface {} interface{}
type route.Addr interface {
	Family() int
}
type route.Message interface {
	Sys() []route.Sys
}
type route.Sys interface {
	SysType() int
}
type route.binaryByteOrder interface {
	PutUint16([]uint8, uint16)
	PutUint32([]uint8, uint32)
	Uint16([]uint8) uint16
	Uint32([]uint8) uint32
	Uint64([]uint8) uint64
}

Structures can be extracted with the struct command. Same as with interfaces, standard library and vendor structures are filtered out but can be included by providing the --std or --vendor flag.

% redress types struct pplauncher
...
type main.bintree struct {
	Func     func() (*main.asset, error)
	Children map[string]*main.bintree
}
...

type main.asset struct {
	bytes []uint8
	info  os.FileInfo
}

type main.bindataFileInfo struct {
	name    string
	size    int64
	mode    uint32
	modTime time.Time
}
...

Methods definitions for the structure is shown by including the --methods flag.

% redress types struct pplauncher --methods
...
type main.asset struct {
	bytes []uint8
	info  os.FileInfo
}

type main.bindataFileInfo struct {
	name    string
	size    int64
	mode    uint32
	modTime time.Time
}
func (main.bindataFileInfo) IsDir() bool
func (main.bindataFileInfo) ModTime() time.Time
func (main.bindataFileInfo) Mode() uint32
func (main.bindataFileInfo) Name() string
func (main.bindataFileInfo) Size() int64
func (main.bindataFileInfo) Sys() interface {}
...

It is also possible to print all types in the binary by using the all command.

Estimating source code layout

One feature of redress is to reconstruct the source code tree layout. This can be done by using the source command. By default, standard library and 3rd party packages are excluded but can be included by providing the flags --std, --vendor, and/or --unknown flags.

The output includes the package name and its folder location at compile time. For each file, the functions defined within are printed. The output also includes auto generated functions produced by the compiler. For each function, redress tries to guess the starting and ending line number.

…

Using redress with radare2

Redress can be executed from within radare2 via r2pipe. If redress is executed with no flags, it performs an automatic analysis of the binary. It will extract all the functions and methods and construct symbol flags for them. It will also extract the types in the binary. It will mark the corresponding _type with this flag to make analysis easier. By doing this, it highlights which actual type is being allocated on the heap for easier analysis. The last thing redress does is to also tell radare2 to analyze the main.init and main.main function recursively.

% r2 pplauncher 
 -- radare2 contributes to the One Byte Per Child foundation.
[0x01055c90]> #!pipe redress r2 init
Compiler version: go1.10 (2018-02-16T16:05:53Z)
39 packages found.
2943 function symbols found
Analyzing all init functions.
Analyzing all main.main.
1717 type symbols found

Redress also support some flags when executed from within radare2. These flags can be used to print the Go definition for a specific type.

[0x01055c90]> #!pipe redress r2 help
Use redress with in r2.

Usage:
  redress r2 [command]

Aliases:
  r2, radare, radare2, r

Available Commands:
  init        Perform the initial analysis
  line        Annotate function with source lines.
  strarr      Print string array.
  type        Print type definition.

Flags:
  -h, --help   help for r2

Use "redress r2 [command] --help" for more information about a command.

Working with types

The type identification by redress makes the analysis easier. In the code snippet below, it can be seen that memory for the type main.bintree is to be allocated.

; CODE XREF from sym.main.init (0x10eb3de)
0x010eb14d      e80ed2f1ff     call sym.runtime.makemap_small
0x010eb152      488b0424       mov rax, qword [rsp]
0x010eb156      4889442440     mov qword [var_40h], rax
0x010eb15b      488d0dbeba02.  lea rcx, sym.type.main.bintree
0x010eb162      48890c24       mov qword [rsp], rcx
0x010eb166      e8155ef2ff     call sym.runtime.newobject

To get the type definition of this type, the address for the flag needs to be known.

:> f~sym.type.main.bintree
0x01116c20 1 sym.type.main.bintree

By executing redress with the type command and the address, the type definition is returned:

> #!pipe redress r2 type 0x01116c20
type main.bintree struct{
	Func func() (*main.asset, error)
	Children map[string]*main.bintree
}

It is possible to chain the two commands:

:> #!pipe redress r2 type `f~sym.type.main.bintree~[0]`
type main.bintree struct{
	Func func() (*main.asset, error)
	Children map[string]*main.bintree
}

A better way is to define a radare2 macro:

:> (type flag,#!pipe redress r2 type `f~$0~[0]`)
:> .(type sym.type.main.bintree)
type main.bintree struct{
	Func func() (*main.asset, error)
	Children map[string]*main.bintree
}