.Net Reactor

Created the Monday 20 June 2022. Updated 10 months, 1 week ago.

.NET Reactor is used to prevent reverse engineering by adding different protection layers to .NET assemblies. Beside standard obfuscation techniques it includes special features like NecroBit, Virtualization, x86 Code Generation or Anti Tampering.

Technique Identifier

U1423

Detection Rules

rule SUSP_OBF_NET_Reactor_Native_Stub_Jan24 {
	meta:
		description = "Detects native packer stub for version 4.5-4.7 of .NET Reactor. A pirated copy of version 4.5 of this commercial obfuscation solution is used by various malware families like BlackBit, RedLine, AgentTesla etc."
		author = "Jonathan Peters"
		date = "2024-01-05"
		reference = "https://notes.netbytesec.com/2023/08/understand-ransomware-ttps-blackbit.html"
		hash = "6e8a7adf680bede7b8429a18815c232004057607fdfbf0f4b0fb1deba71c5df7"
		score = 70
	strings:
		$op = {C6 44 24 18 E0 C6 44 24 19 3B C6 44 24 1A 8D C6 44 24 1B 2A C6 44 24 1C A2 C6 44 24 1D 2A C6 44 24 1E 2A C6 44 24 1F 41 C6 44 24 20 D3 C6 44 24 21 20 C6 44 24 22 64 C6 44 24 23 06 C6 44 24 24 8A C6 44 24 25 F7 C6 44 24 26 3D C6 44 24 27 9D C6 44 24 28 D9 C6 44 24 29 EE C6 44 24 2A 15 C6 44 24 2B 68 C6 44 24 2C F4 C6 44 24 2D 76 C6 44 24 2E B9 C6 44 24 2F 34 C6 44 24 30 BF C6 44 24 31 1E C6 44 24 32 E7 C6 44 24 33 78 C6 44 24 34 98 C6 44 24 35 E9 C6 44 24 36 6F C6 44 24 37 B4}
	condition:
		for any i in (0..pe.number_of_resources-1) : (pe.resources[i].name_string == "_\x00_\x00")
		and $op
}

rule SUSP_OBF_NET_Reactor_Indicators_Jan24
{
	meta:
		description = "Detects indicators of .NET Reactors managed obfuscation. Reactor is a commercial obfuscation solution, pirated versions are often abused by threat actors."
		author = "Jonathan Peters"
		date = "2024-01-09"
		reference = "https://www.eziriz.com/dotnet_reactor.htm"
		hash = "be842a9de19cfbf42ea5a94e3143d58390a1abd1e72ebfec5deeb8107dddf038"
		score = 65
	strings:
		$ = { 33 7B 00 [9] 00 2D 00 [9] 00 2D 00 [9] 00 2D 00 [9] 00 7D 00 }
		$ = { 3C 50 72 69 76 61 74 65 49 6D 70 6C 65 6D 65 6E 74 61 74 69 6F 6E 44 65 74 61 69 6C 73 3E 7B [8] 2D [4] 2D [4] 2D [4] 2D [12] 7D }
		$ = { 3C 4D 6F 64 75 6C 65 3E 7B [8] 2D [4] 2D [4] 2D [4] 2D [12] 7D }
	condition:
      uint16(0) == 0x5a4d
		and 2 of them
}

Contributor

Jonathan Peters

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

.NET Reactor - .NET Protection, .NET Obfuscator and Licensing