[DETECTION] Unknown packer (classes.dex) detection

[ReBensk]

Samples

https://www.virustotal.com/gui/file/b8f8948187846371eb32b2d7ef4f537c94997329e08d762b9ac6b3bfcbc86993/detection
https://www.virustotal.com/gui/file/fdf5b6930d38da33ec117d7c0f83f142db1c33013d020f0ab4801d1fd781f552/detection

APKiD current results...

[+] APKiD 2.1.5 :: from RedNaga :: rednaga.io
[] ./com.rihjzvyvdmwsz.wfglmgpoijgnc.apk!classes.dex
|-> compiler : dexlib 2.x
[] ./com.zxqlzbjtkwugo.oekyzihfuspse.apk!classes.dex
|-> compiler : dexlib 2.x
[*] ./classes.dex
|-> compiler : dexlib 2.x

Additional context
Classes.dex file is packed with a custom packer.
From the Classes.dex file structure:a
data_size(offset 0x68) +data_off(offset 0x6C) > file_size (offset 0x20)

[enovella]

Hi @ReBensk ,

I don't have a VT subscription, could you share these files in a ZIP file over here? Thanks

Edu

[ReBensk]

Sample1.zip
Sample2.zip
Samples Uploaded

[enovella]

Hi @ReBensk ,

I will try to create rules for this packer. Could you tell me unique patterns in these samples? And a made up name for it too?

[ReBensk]

rule Detect_Custom_Packer {
strings:
$aes_type = "AESTYPE"
$aes_string = "AES"
$encodeStr_func = "encodeStr"
$g_pass = "globalPass"
$e_pass = "encodePass"
$encodeToMD516_func = "encodeToMD516"
$encodeToMD5 = "encodeToMD5"

condition:
    any of them

}

[enovella]

rule Detect_Custom_Packer { strings: $aes_type = "AESTYPE" $aes_string = "AES" $encodeStr_func = "encodeStr" $g_pass = "globalPass" $e_pass = "encodePass" $encodeToMD516_func = "encodeToMD516" $encodeToMD5 = "encodeToMD5"

condition:
    any of them

}

This rule will produce many false positives due to the condition any of them with non-unique strings such as AES. What about all of them or 5 of them? Do you have opcodes, asset files, or other fingerprints instead of only-strings?

Lately, I don't get free time to look into this, feel free to pull-request any rule you want to and I will attempt reviewing it. Thanks for opening this ticket.

--Edu

[enovella]

@ReBensk Can you re-open the ticket and create this rule into a PR?

[ReBensk]

@ReBensk Can you re-open the ticket and create this rule into a PR?
Please refer the below ticket and created a new rule
#370