SYMBOLCOMMON_NAMEaka. SYNONYMS
win.tflower (Back to overview)

TFlower

VTCollection    

TFlower is a new ransomware targeting mostly corporate networks discovered in August, 2019. It is reportedly installed on networks by attackers after they gain access via RDP. TFlower displays a console showing activity being performed by the ransomware when it encrypts a machine, further indicating that this ransomware is triggered by the attacker post compromise, similar to Samsam/Samas in terms of TTP. Once encryption is started, the ransomware will conduct a status report to an apparently hard-coded C2. Shadow copies are deleted and the Windows 10 repair environment is disabled by this ransomware. This malware also will terminate any running Outlook.exe process so that the mail files can be encrypted. This ransomware does not add an extention to encrypted files, but prepends the marker "*tflower" and what may be the encrypted encryption key for the file to each affected file. Once encryption is completed, another status report is sent to the C2 server.

References
2021-03-03SYGNIAAmitai Ben Shushan, Amnon Kushnir, Boaz Wasserman, Martin Korman, Noam Lifshitz
Lazarus Group’s MATA Framework Leveraged to Deploy TFlower Ransomware
Dacls Dacls Dacls TFlower
2019-09-20Canadian Centre for Cyber SecurityCanadian Centre for Cyber Security
TFlower Ransomware Campaign
TFlower
2019-09-17Bleeping ComputerLawrence Abrams
TFlower Ransomware - The Latest Attack Targeting Businesses
TFlower
Yara Rules
[TLP:WHITE] win_tflower_auto (20251219 | Detects win.tflower.)
rule win_tflower_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2026-01-05"
        version = "1"
        description = "Detects win.tflower."
        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.tflower"
        malpedia_rule_date = "20260105"
        malpedia_hash = "19b79e7cab4eaf532122e5b45a77dd8f6bb5cc79"
        malpedia_version = "20251219"
        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 = { 0001 0200 0103 0303 }
            // n = 4, score = 200
            //   0001                 | add                 byte ptr [ecx], al
            //   0200                 | add                 al, byte ptr [eax]
            //   0103                 | add                 dword ptr [ebx], eax
            //   0303                 | add                 eax, dword ptr [ebx]

        $sequence_1 = { 000f 7708 0001 7708 }
            // n = 4, score = 200
            //   000f                 | add                 byte ptr [edi], cl
            //   7708                 | ja                  0xa
            //   0001                 | add                 byte ptr [ecx], al
            //   7708                 | ja                  0xa

        $sequence_2 = { 0002 7408 00f7 7308 }
            // n = 4, score = 200
            //   0002                 | add                 byte ptr [edx], al
            //   7408                 | je                  0xa
            //   00f7                 | add                 bh, dh
            //   7308                 | jae                 0xa

        $sequence_3 = { 89442414 8b06 83f804 0f8728010000 ff2485249d4a00 6a02 6a01 }
            // n = 7, score = 200
            //   89442414             | mov                 dword ptr [esp + 0x14], eax
            //   8b06                 | mov                 eax, dword ptr [esi]
            //   83f804               | cmp                 eax, 4
            //   0f8728010000         | ja                  0x12e
            //   ff2485249d4a00       | jmp                 dword ptr [eax*4 + 0x4a9d24]
            //   6a02                 | push                2
            //   6a01                 | push                1

        $sequence_4 = { 001a 0c05 003c0c 05004e0c05 }
            // n = 4, score = 200
            //   001a                 | add                 byte ptr [edx], bl
            //   0c05                 | or                  al, 5
            //   003c0c               | add                 byte ptr [esp + ecx], bh
            //   05004e0c05           | add                 eax, 0x50c4e00

        $sequence_5 = { 8b148dc0064f00 331485c0024f00 8bc3 c1e808 }
            // n = 4, score = 200
            //   8b148dc0064f00       | mov                 edx, dword ptr [ecx*4 + 0x4f06c0]
            //   331485c0024f00       | xor                 edx, dword ptr [eax*4 + 0x4f02c0]
            //   8bc3                 | mov                 eax, ebx
            //   c1e808               | shr                 eax, 8

        $sequence_6 = { 83fa07 8b542410 775e 8b6c2414 ff24ad9ce34600 0fb679ff }
            // n = 6, score = 200
            //   83fa07               | cmp                 edx, 7
            //   8b542410             | mov                 edx, dword ptr [esp + 0x10]
            //   775e                 | ja                  0x60
            //   8b6c2414             | mov                 ebp, dword ptr [esp + 0x14]
            //   ff24ad9ce34600       | jmp                 dword ptr [ebp*4 + 0x46e39c]
            //   0fb679ff             | movzx               edi, byte ptr [ecx - 1]

        $sequence_7 = { 000b 8605???????? 007885 0500788605 }
            // n = 4, score = 200
            //   000b                 | add                 byte ptr [ebx], cl
            //   8605????????         |                     
            //   007885               | add                 byte ptr [eax - 0x7b], bh
            //   0500788605           | add                 eax, 0x5867800

        $sequence_8 = { 33148520c54e00 33f2 2bde d3c3 8bc3 }
            // n = 5, score = 200
            //   33148520c54e00       | xor                 edx, dword ptr [eax*4 + 0x4ec520]
            //   33f2                 | xor                 esi, edx
            //   2bde                 | sub                 ebx, esi
            //   d3c3                 | rol                 ebx, cl
            //   8bc3                 | mov                 eax, ebx

        $sequence_9 = { 0010 740b 0021 740b }
            // n = 4, score = 200
            //   0010                 | add                 byte ptr [eax], dl
            //   740b                 | je                  0xd
            //   0021                 | add                 byte ptr [ecx], ah
            //   740b                 | je                  0xd

        $sequence_10 = { c745e0787f4b00 e9???????? c745e0647f4b00 e9???????? c745dc02000000 }
            // n = 5, score = 200
            //   c745e0787f4b00       | mov                 dword ptr [ebp - 0x20], 0x4b7f78
            //   e9????????           |                     
            //   c745e0647f4b00       | mov                 dword ptr [ebp - 0x20], 0x4b7f64
            //   e9????????           |                     
            //   c745dc02000000       | mov                 dword ptr [ebp - 0x24], 2

        $sequence_11 = { 0001 7708 00f3 7608 }
            // n = 4, score = 200
            //   0001                 | add                 byte ptr [ecx], al
            //   7708                 | ja                  0xa
            //   00f3                 | add                 bl, dh
            //   7608                 | jbe                 0xa

        $sequence_12 = { 0008 7408 0002 7408 }
            // n = 4, score = 200
            //   0008                 | add                 byte ptr [eax], cl
            //   7408                 | je                  0xa
            //   0002                 | add                 byte ptr [edx], al
            //   7408                 | je                  0xa

        $sequence_13 = { c1e818 8b4d2c c1eb10 03148520c14e00 0fb6c3 8b5d28 }
            // n = 6, score = 200
            //   c1e818               | shr                 eax, 0x18
            //   8b4d2c               | mov                 ecx, dword ptr [ebp + 0x2c]
            //   c1eb10               | shr                 ebx, 0x10
            //   03148520c14e00       | add                 edx, dword ptr [eax*4 + 0x4ec120]
            //   0fb6c3               | movzx               eax, bl
            //   8b5d28               | mov                 ebx, dword ptr [ebp + 0x28]

        $sequence_14 = { 0fb6c0 8b0c8d20ed4e00 330c8520f14e00 8bc3 c1e818 c1eb10 }
            // n = 6, score = 200
            //   0fb6c0               | movzx               eax, al
            //   8b0c8d20ed4e00       | mov                 ecx, dword ptr [ecx*4 + 0x4eed20]
            //   330c8520f14e00       | xor                 ecx, dword ptr [eax*4 + 0x4ef120]
            //   8bc3                 | mov                 eax, ebx
            //   c1e818               | shr                 eax, 0x18
            //   c1eb10               | shr                 ebx, 0x10

        $sequence_15 = { 0fbec0 8d89f8feffff 8d0c48 3b0c95788f4f00 }
            // n = 4, score = 200
            //   0fbec0               | movsx               eax, al
            //   8d89f8feffff         | lea                 ecx, [ecx - 0x108]
            //   8d0c48               | lea                 ecx, [eax + ecx*2]
            //   3b0c95788f4f00       | cmp                 ecx, dword ptr [edx*4 + 0x4f8f78]

    condition:
        7 of them and filesize < 6578176
}
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