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 = "2026-05-04" 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 = "20260422" malpedia_hash = "a182e35da64e6d71cb55f125c4d4225196523f14" malpedia_version = "20260504" 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 = { 4c8bc6 33d2 410fbe00 49ffc0 d3ca 03d0 4183ef01 } // n = 7, score = 1300 // 4c8bc6 | dec esp // 33d2 | mov eax, esi // 410fbe00 | xor edx, edx // 49ffc0 | inc ecx // d3ca | movsx eax, byte ptr [eax] // 03d0 | dec ecx // 4183ef01 | inc eax $sequence_1 = { 33f6 8d6e20 8bcd e8???????? } // n = 4, score = 1300 // 33f6 | movsx eax, byte ptr [eax] // 8d6e20 | dec ecx // 8bcd | inc eax // e8???????? | $sequence_2 = { ff15???????? 448bf0 4533c9 4533c0 } // n = 4, score = 1300 // ff15???????? | // 448bf0 | inc ecx // 4533c9 | movsx eax, byte ptr [eax] // 4533c0 | dec ecx $sequence_3 = { 458d7ee0 418bd7 ff15???????? 4821742420 } // n = 4, score = 1300 // 458d7ee0 | dec esp // 418bd7 | mov eax, esi // ff15???????? | // 4821742420 | xor edx, edx $sequence_4 = { 4883ec28 4885c9 7402 ffd1 } // n = 4, score = 1300 // 4883ec28 | sar edx, 0xb // 4885c9 | mov eax, edx // 7402 | shr eax, 0x1f // ffd1 | add edx, eax $sequence_5 = { 8bc2 c1e81f 03d0 69c2890e0000 } // n = 4, score = 1300 // 8bc2 | mov eax, edx // c1e81f | shr eax, 0x1f // 03d0 | add edx, eax // 69c2890e0000 | imul eax, edx, 0xe89 $sequence_6 = { 458bc6 33d2 488bc8 e8???????? 4533c9 4533c0 33d2 } // n = 7, score = 1300 // 458bc6 | inc ecx // 33d2 | sub edi, 1 // 488bc8 | jne 0xfffffff7 // e8???????? | // 4533c9 | sar edx, 0xb // 4533c0 | mov eax, edx // 33d2 | shr eax, 0x1f $sequence_7 = { 418bc0 f7e9 03d1 c1fa0b 8bc2 } // n = 5, score = 1300 // 418bc0 | xor eax, eax // f7e9 | xor edx, edx // 03d1 | add edx, ecx // c1fa0b | sar edx, 0xb // 8bc2 | mov eax, edx $sequence_8 = { 83e13f 6bc930 53 56 8b0485808e4100 33db 8b7508 } // n = 7, score = 200 // 83e13f | and ecx, 0x3f // 6bc930 | imul ecx, ecx, 0x30 // 53 | push ebx // 56 | push esi // 8b0485808e4100 | mov eax, dword ptr [eax*4 + 0x418e80] // 33db | xor ebx, ebx // 8b7508 | mov esi, dword ptr [ebp + 8] $sequence_9 = { 660fd60f 8d7f08 8b048d34024100 ffe0 f7c703000000 7413 8a06 } // n = 7, score = 200 // 660fd60f | movq qword ptr [edi], xmm1 // 8d7f08 | lea edi, [edi + 8] // 8b048d34024100 | mov eax, dword ptr [ecx*4 + 0x410234] // ffe0 | jmp eax // f7c703000000 | test edi, 3 // 7413 | je 0x15 // 8a06 | mov al, byte ptr [esi] $sequence_10 = { 898850030000 8b4508 59 c74048f0844100 } // n = 4, score = 200 // 898850030000 | mov dword ptr [eax + 0x350], ecx // 8b4508 | mov eax, dword ptr [ebp + 8] // 59 | pop ecx // c74048f0844100 | mov dword ptr [eax + 0x48], 0x4184f0 $sequence_11 = { 33c9 8b450c 0fb684c8981a4100 c1e804 } // n = 4, score = 200 // 33c9 | xor ecx, ecx // 8b450c | mov eax, dword ptr [ebp + 0xc] // 0fb684c8981a4100 | movzx eax, byte ptr [eax + ecx*8 + 0x411a98] // c1e804 | shr eax, 4 $sequence_12 = { 75be ddd8 db2d???????? b802000000 833d????????00 0f85a0110000 8d0dc0584100 } // n = 7, score = 200 // 75be | jne 0xffffffc0 // ddd8 | fstp st(0) // db2d???????? | // b802000000 | mov eax, 2 // 833d????????00 | // 0f85a0110000 | jne 0x11a6 // 8d0dc0584100 | lea ecx, [0x4158c0] $sequence_13 = { 6bd030 895de4 8b049d808e4100 8945d4 8955e8 } // n = 5, score = 200 // 6bd030 | imul edx, eax, 0x30 // 895de4 | mov dword ptr [ebp - 0x1c], ebx // 8b049d808e4100 | mov eax, dword ptr [ebx*4 + 0x418e80] // 8945d4 | mov dword ptr [ebp - 0x2c], eax // 8955e8 | mov dword ptr [ebp - 0x18], edx $sequence_14 = { 57 8bf9 0f1f440000 6a00 6a00 57 } // n = 6, score = 200 // 57 | push edi // 8bf9 | mov edi, ecx // 0f1f440000 | nop dword ptr [eax + eax] // 6a00 | push 0 // 6a00 | push 0 // 57 | push edi $sequence_15 = { 6a00 50 6a0c 53 56 ff15???????? } // n = 6, score = 200 // 6a00 | push 0 // 50 | push eax // 6a0c | push 0xc // 53 | push ebx // 56 | push esi // ff15???????? | condition: 7 of them and filesize < 286720 }
If your designated proposal does not fit in any other category, feel free to write a free-text in the comment field below. Changes regarding references should be proposed on the Malpedia library page.
Your suggestion will be reviewed before being published. Thank you for contributing!
YYYY-MM-DD
YYYY-MM
YYYY
