Actor(s): APT41
According to FireEye, CROSSWALK is a skeletal, modular backdoor capable of system survey and adding modules in response to C&C replies.
rule win_crosswalk_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" version = "1" description = "Detects win.crosswalk." info = "autogenerated rule brought to you by yara-signator" tool = "yara-signator v0.6.0" signator_config = "callsandjumps;datarefs;binvalue" malpedia_reference = "https://malpedia.caad.fkie.fraunhofer.de/details/win.crosswalk" malpedia_rule_date = "20230705" malpedia_hash = "42d0574f4405bd7d2b154d321d345acb18834a41" malpedia_version = "20230715" malpedia_license = "CC BY-SA 4.0" malpedia_sharing = "TLP:WHITE" /* DISCLAIMER * The strings used in this rule have been automatically selected from the * disassembly of memory dumps and unpacked files, using YARA-Signator. * The code and documentation is published here: * https://github.com/fxb-cocacoding/yara-signator * As Malpedia is used as data source, please note that for a given * number of families, only single samples are documented. * This likely impacts the degree of generalization these rules will offer. * Take the described generation method also into consideration when you * apply the rules in your use cases and assign them confidence levels. */ strings: $sequence_0 = { 33f6 8d6e20 8bcd e8???????? } // n = 4, score = 1300 // 33f6 | add edx, eax // 8d6e20 | inc ecx // 8bcd | sub edi, 1 // e8???????? | $sequence_1 = { 4883ec28 4885c9 7402 ffd1 } // n = 4, score = 1300 // 4883ec28 | inc ecx // 4885c9 | mov eax, eax // 7402 | imul ecx // ffd1 | add edx, ecx $sequence_2 = { ff15???????? 448bf0 4533c9 4533c0 } // n = 4, score = 1300 // ff15???????? | // 448bf0 | mov eax, esi // 4533c9 | xor edx, edx // 4533c0 | inc ecx $sequence_3 = { 458d7ee0 418bd7 ff15???????? 4821742420 } // n = 4, score = 1300 // 458d7ee0 | imul ecx // 418bd7 | add edx, ecx // ff15???????? | // 4821742420 | sar edx, 0xb $sequence_4 = { 03d1 c1fa0b 8bc2 c1e81f 03d0 69c2890e0000 } // n = 6, score = 1300 // 03d1 | add edx, ecx // c1fa0b | sar edx, 0xb // 8bc2 | mov eax, edx // c1e81f | shr eax, 0x1f // 03d0 | add edx, eax // 69c2890e0000 | imul eax, edx, 0xe89 $sequence_5 = { 458bc6 33d2 488bc8 e8???????? 4533c9 4533c0 33d2 } // n = 7, score = 1300 // 458bc6 | dec ecx // 33d2 | inc eax // 488bc8 | ror edx, cl // e8???????? | // 4533c9 | add edx, eax // 4533c0 | sar edx, 0xb // 33d2 | mov eax, edx $sequence_6 = { 418bc0 f7e9 03d1 c1fa0b } // n = 4, score = 1300 // 418bc0 | sub edi, 1 // f7e9 | xor edx, edx // 03d1 | inc ecx // c1fa0b | movsx eax, byte ptr [eax] $sequence_7 = { 33d2 410fbe00 49ffc0 d3ca 03d0 4183ef01 75ef } // n = 7, score = 1300 // 33d2 | mov eax, edx // 410fbe00 | xor edx, edx // 49ffc0 | inc ecx // d3ca | movsx eax, byte ptr [eax] // 03d0 | dec ecx // 4183ef01 | inc eax // 75ef | ror edx, cl $sequence_8 = { c745e0185b4100 e9???????? c745e0145b4100 eba2 894ddc } // n = 5, score = 200 // c745e0185b4100 | mov dword ptr [ebp - 0x20], 0x415b18 // e9???????? | // c745e0145b4100 | mov dword ptr [ebp - 0x20], 0x415b14 // eba2 | jmp 0xffffffa4 // 894ddc | mov dword ptr [ebp - 0x24], ecx $sequence_9 = { 0f84b2000000 85f6 0f84aa000000 6a00 56 ff15???????? 6a00 } // n = 7, score = 200 // 0f84b2000000 | je 0xb8 // 85f6 | test esi, esi // 0f84aa000000 | je 0xb0 // 6a00 | push 0 // 56 | push esi // ff15???????? | // 6a00 | push 0 $sequence_10 = { 83e801 0f859b010000 c745e0185b4100 8b4508 8bcf 8b7510 } // n = 6, score = 200 // 83e801 | sub eax, 1 // 0f859b010000 | jne 0x1a1 // c745e0185b4100 | mov dword ptr [ebp - 0x20], 0x415b18 // 8b4508 | mov eax, dword ptr [ebp + 8] // 8bcf | mov ecx, edi // 8b7510 | mov esi, dword ptr [ebp + 0x10] $sequence_11 = { c1f906 6bd030 8b45fc 03148d808e4100 8b00 } // n = 5, score = 200 // c1f906 | sar ecx, 6 // 6bd030 | imul edx, eax, 0x30 // 8b45fc | mov eax, dword ptr [ebp - 4] // 03148d808e4100 | add edx, dword ptr [ecx*4 + 0x418e80] // 8b00 | mov eax, dword ptr [eax] $sequence_12 = { 6bf630 8b0c8d808e4100 80643128fd 5f } // n = 4, score = 200 // 6bf630 | imul esi, esi, 0x30 // 8b0c8d808e4100 | mov ecx, dword ptr [ecx*4 + 0x418e80] // 80643128fd | and byte ptr [ecx + esi + 0x28], 0xfd // 5f | pop edi $sequence_13 = { 6af6 ff15???????? 8b04bd808e4100 834c0318ff 33c0 eb16 } // n = 6, score = 200 // 6af6 | push -0xa // ff15???????? | // 8b04bd808e4100 | mov eax, dword ptr [edi*4 + 0x418e80] // 834c0318ff | or dword ptr [ebx + eax + 0x18], 0xffffffff // 33c0 | xor eax, eax // eb16 | jmp 0x18 $sequence_14 = { 03348d808e4100 837e18ff 740c 837e18fe 7406 } // n = 5, score = 200 // 03348d808e4100 | add esi, dword ptr [ecx*4 + 0x418e80] // 837e18ff | cmp dword ptr [esi + 0x18], -1 // 740c | je 0xe // 837e18fe | cmp dword ptr [esi + 0x18], -2 // 7406 | je 8 $sequence_15 = { be???????? c745ec24234100 57 8d3c85fcffffff 8975cc 8d041f 8975d0 } // n = 7, score = 200 // be???????? | // c745ec24234100 | mov dword ptr [ebp - 0x14], 0x412324 // 57 | push edi // 8d3c85fcffffff | lea edi, [eax*4 - 4] // 8975cc | mov dword ptr [ebp - 0x34], esi // 8d041f | lea eax, [edi + ebx] // 8975d0 | mov dword ptr [ebp - 0x30], esi condition: 7 of them and filesize < 286720 }
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