Analysis

  • max time kernel
    150s
  • max time network
    151s
  • platform
    windows10-2004_x64
  • resource
    win10v2004-20240426-en
  • resource tags

    arch:x64arch:x86image:win10v2004-20240426-enlocale:en-usos:windows10-2004-x64system
  • submitted
    22-05-2024 14:47

General

  • Target

    e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374.jar

  • Size

    558KB

  • MD5

    bcba7d102e446ddc938ac77dc6839957

  • SHA1

    cfec4feb6928e64b4f687b251226fea8ed711272

  • SHA256

    e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374

  • SHA512

    413e11469477db47ae5e9cda764fe03bb03ce0c5589f92dd71b55078ed118f3f02cecc9d047142233c239ffd7c6ba44c5ac3c4337046e05311e9d4ff17a0fa57

  • SSDEEP

    12288:TEeO4P145DUpuLHpDK5j+gXAhfpJEFqwM:TEept4mpuFaq/hb

Malware Config

Signatures

  • STRRAT

    STRRAT is a remote access tool than can steal credentials and log keystrokes.

  • Drops startup file 1 IoCs
  • Loads dropped DLL 1 IoCs
  • Modifies file permissions 1 TTPs 1 IoCs
  • Adds Run key to start application 2 TTPs 2 IoCs
  • Looks up external IP address via web service 1 IoCs

    Uses a legitimate IP lookup service to find the infected system's external IP.

  • Creates scheduled task(s) 1 TTPs 1 IoCs

    Schtasks is often used by malware for persistence or to perform post-infection execution.

  • Suspicious use of AdjustPrivilegeToken 64 IoCs
  • Suspicious use of WriteProcessMemory 26 IoCs
  • Uses Task Scheduler COM API 1 TTPs

    The Task Scheduler COM API can be used to schedule applications to run on boot or at set times.

Processes

  • C:\Program Files (x86)\Common Files\Oracle\Java\javapath\java.exe
    java -jar C:\Users\Admin\AppData\Local\Temp\e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374.jar
    1⤵
    • Suspicious use of WriteProcessMemory
    PID:1704
    • C:\Windows\system32\icacls.exe
      C:\Windows\system32\icacls.exe C:\ProgramData\Oracle\Java\.oracle_jre_usage /grant "everyone":(OI)(CI)M
      2⤵
      • Modifies file permissions
      PID:448
    • C:\Program Files\Java\jre-1.8\bin\java.exe
      "C:\Program Files\Java\jre-1.8\bin\java.exe" -jar "C:\Users\Admin\e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374.jar"
      2⤵
      • Drops startup file
      • Adds Run key to start application
      • Suspicious use of WriteProcessMemory
      PID:4292
      • C:\Windows\SYSTEM32\cmd.exe
        cmd /c schtasks /create /sc minute /mo 30 /tn Skype /tr "C:\Users\Admin\AppData\Roaming\e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374.jar"
        3⤵
        • Suspicious use of WriteProcessMemory
        PID:4816
        • C:\Windows\system32\schtasks.exe
          schtasks /create /sc minute /mo 30 /tn Skype /tr "C:\Users\Admin\AppData\Roaming\e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374.jar"
          4⤵
          • Creates scheduled task(s)
          PID:3448
      • C:\Program Files\Java\jre-1.8\bin\java.exe
        "C:\Program Files\Java\jre-1.8\bin\java.exe" -jar "C:\Users\Admin\AppData\Roaming\e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374.jar"
        3⤵
        • Loads dropped DLL
        • Suspicious use of WriteProcessMemory
        PID:1860
        • C:\Windows\SYSTEM32\cmd.exe
          cmd.exe /c "wmic /node:. /namespace:'\\root\cimv2' path win32_logicaldisk get volumeserialnumber /format:list"
          4⤵
          • Suspicious use of WriteProcessMemory
          PID:4588
          • C:\Windows\System32\Wbem\WMIC.exe
            wmic /node:. /namespace:'\\root\cimv2' path win32_logicaldisk get volumeserialnumber /format:list
            5⤵
            • Suspicious use of AdjustPrivilegeToken
            PID:1032
        • C:\Windows\SYSTEM32\cmd.exe
          cmd.exe /c "wmic /node:. /namespace:'\\root\cimv2' path win32_operatingsystem get caption,OSArchitecture /format:list"
          4⤵
          • Suspicious use of WriteProcessMemory
          PID:556
          • C:\Windows\System32\Wbem\WMIC.exe
            wmic /node:. /namespace:'\\root\cimv2' path win32_operatingsystem get caption,OSArchitecture /format:list
            5⤵
            • Suspicious use of AdjustPrivilegeToken
            PID:2796
        • C:\Windows\SYSTEM32\cmd.exe
          cmd.exe /c "wmic /node:. /namespace:'\\root\cimv2' path win32_operatingsystem get version /format:list"
          4⤵
          • Suspicious use of WriteProcessMemory
          PID:4572
          • C:\Windows\System32\Wbem\WMIC.exe
            wmic /node:. /namespace:'\\root\cimv2' path win32_operatingsystem get version /format:list
            5⤵
              PID:384
          • C:\Windows\SYSTEM32\cmd.exe
            cmd.exe /c "wmic /node:localhost /namespace:'\\root\securitycenter2' path antivirusproduct get displayname /format:list"
            4⤵
            • Suspicious use of WriteProcessMemory
            PID:4496
            • C:\Windows\System32\Wbem\WMIC.exe
              wmic /node:localhost /namespace:'\\root\securitycenter2' path antivirusproduct get displayname /format:list
              5⤵
                PID:868

      Network

      MITRE ATT&CK Enterprise v15

      Replay Monitor

      Loading Replay Monitor...

      Downloads

      • C:\ProgramData\Oracle\Java\.oracle_jre_usage\3903daac9bc4a3b7.timestamp

        Filesize

        46B

        MD5

        287dea0e4f77e107bcdc1954f7cee5b2

        SHA1

        af338e7c2ae24a35214a1db90ee45cfe6d51a734

        SHA256

        5481c237b517574bc816ca9344d4798b11c86db353eb1f59261a5b07299f1bb6

        SHA512

        11d005a62d92cb04a3c560412ebc562bf2e02629357c7f31486efaa7906d19fbe24819774ac717cb2d3c7207127579ff5c082ba8f7d2cbe4ec6ca9f713ec492c

      • C:\ProgramData\Oracle\Java\.oracle_jre_usage\3903daac9bc4a3b7.timestamp

        MD5

        d41d8cd98f00b204e9800998ecf8427e

        SHA1

        da39a3ee5e6b4b0d3255bfef95601890afd80709

        SHA256

        e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

        SHA512

        cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e

      • C:\Users\Admin\AppData\Local\Temp\jna-63116079\jna7806504339526590737.dll

        Filesize

        241KB

        MD5

        e02979ecd43bcc9061eb2b494ab5af50

        SHA1

        3122ac0e751660f646c73b10c4f79685aa65c545

        SHA256

        a66959bec2ef5af730198db9f3b3f7cab0d4ae70ce01bec02bf1d738e6d1ee7a

        SHA512

        1e6f7dcb6a557c9b896412a48dd017c16f7a52fa2b9ab513593c9ecd118e86083979821ca7a3e2f098ee349200c823c759cec6599740dd391cb5f354dc29b372

      • C:\Users\Admin\AppData\Roaming\Microsoft\Crypto\RSA\S-1-5-21-1162180587-977231257-2194346871-1000\83aa4cc77f591dfc2374580bbd95f6ba_44d43ff8-91cd-4ca7-92c9-6495b4f546fa

        Filesize

        45B

        MD5

        c8366ae350e7019aefc9d1e6e6a498c6

        SHA1

        5731d8a3e6568a5f2dfbbc87e3db9637df280b61

        SHA256

        11e6aca8e682c046c83b721eeb5c72c5ef03cb5936c60df6f4993511ddc61238

        SHA512

        33c980d5a638bfc791de291ebf4b6d263b384247ab27f261a54025108f2f85374b579a026e545f81395736dd40fa4696f2163ca17640dd47f1c42bc9971b18cd

      • C:\Users\Admin\e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374.jar

        Filesize

        558KB

        MD5

        bcba7d102e446ddc938ac77dc6839957

        SHA1

        cfec4feb6928e64b4f687b251226fea8ed711272

        SHA256

        e6e7a195132e49584dd2015d1dcb43e547cd55c1a772f3509b126fdc555a8374

        SHA512

        413e11469477db47ae5e9cda764fe03bb03ce0c5589f92dd71b55078ed118f3f02cecc9d047142233c239ffd7c6ba44c5ac3c4337046e05311e9d4ff17a0fa57

      • C:\Users\Admin\lib\jna-5.5.0.jar

        Filesize

        1.4MB

        MD5

        acfb5b5fd9ee10bf69497792fd469f85

        SHA1

        0e0845217c4907822403912ad6828d8e0b256208

        SHA256

        b308faebfe4ed409de8410e0a632d164b2126b035f6eacff968d3908cafb4d9e

        SHA512

        e52575f58a195ceb3bd16b9740eadf5bc5b1d4d63c0734e8e5fd1d1776aa2d068d2e4c7173b83803f95f72c0a6759ae1c9b65773c734250d4cfcdf47a19f82aa

      • C:\Users\Admin\lib\jna-platform-5.5.0.jar

        Filesize

        2.6MB

        MD5

        2f4a99c2758e72ee2b59a73586a2322f

        SHA1

        af38e7c4d0fc73c23ecd785443705bfdee5b90bf

        SHA256

        24d81621f82ac29fcdd9a74116031f5907a2343158e616f4573bbfa2434ae0d5

        SHA512

        b860459a0d3bf7ccb600a03aa1d2ac0358619ee89b2b96ed723541e182b6fdab53aefef7992acb4e03fca67aa47cbe3907b1e6060a60b57ed96c4e00c35c7494

      • C:\Users\Admin\lib\sqlite-jdbc-3.14.2.1.jar

        Filesize

        4.1MB

        MD5

        b33387e15ab150a7bf560abdc73c3bec

        SHA1

        66b8075784131f578ef893fd7674273f709b9a4c

        SHA256

        2eae3dea1c3dde6104c49f9601074b6038ff6abcf3be23f4b56f6720a4f6a491

        SHA512

        25cfb0d6ce35d0bcb18527d3aa12c63ecb2d9c1b8b78805d1306e516c13480b79bb0d74730aa93bd1752f9ac2da9fdd51781c48844cea2fd52a06c62852c8279

      • C:\Users\Admin\lib\system-hook-3.5.jar

        Filesize

        772KB

        MD5

        e1aa38a1e78a76a6de73efae136cdb3a

        SHA1

        c463da71871f780b2e2e5dba115d43953b537daf

        SHA256

        2ddda8af6faef8bde46acf43ec546603180bcf8dcb2e5591fff8ac9cd30b5609

        SHA512

        fee16fe9364926ec337e52f551fd62ed81984808a847de2fd68ff29b6c5da0dcc04ef6d8977f0fe675662a7d2ea1065cdcdd2a5259446226a7c7c5516bd7d60d

      • memory/1704-86-0x0000026D80320000-0x0000026D80330000-memory.dmp

        Filesize

        64KB

      • memory/1704-17-0x0000026D802A0000-0x0000026D802B0000-memory.dmp

        Filesize

        64KB

      • memory/1704-24-0x0000026D802C0000-0x0000026D802D0000-memory.dmp

        Filesize

        64KB

      • memory/1704-25-0x0000026D802D0000-0x0000026D802E0000-memory.dmp

        Filesize

        64KB

      • memory/1704-28-0x0000026D802E0000-0x0000026D802F0000-memory.dmp

        Filesize

        64KB

      • memory/1704-29-0x0000026D802F0000-0x0000026D80300000-memory.dmp

        Filesize

        64KB

      • memory/1704-31-0x0000026D80300000-0x0000026D80310000-memory.dmp

        Filesize

        64KB

      • memory/1704-35-0x0000026D80310000-0x0000026D80320000-memory.dmp

        Filesize

        64KB

      • memory/1704-34-0x0000026D80000000-0x0000026D80270000-memory.dmp

        Filesize

        2.4MB

      • memory/1704-37-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-39-0x0000026D80330000-0x0000026D80340000-memory.dmp

        Filesize

        64KB

      • memory/1704-38-0x0000026D80320000-0x0000026D80330000-memory.dmp

        Filesize

        64KB

      • memory/1704-47-0x0000026D80350000-0x0000026D80360000-memory.dmp

        Filesize

        64KB

      • memory/1704-46-0x0000026D80340000-0x0000026D80350000-memory.dmp

        Filesize

        64KB

      • memory/1704-49-0x0000026D80270000-0x0000026D80280000-memory.dmp

        Filesize

        64KB

      • memory/1704-51-0x0000026D80360000-0x0000026D80370000-memory.dmp

        Filesize

        64KB

      • memory/1704-50-0x0000026D802A0000-0x0000026D802B0000-memory.dmp

        Filesize

        64KB

      • memory/1704-55-0x0000026D80370000-0x0000026D80380000-memory.dmp

        Filesize

        64KB

      • memory/1704-54-0x0000026D80290000-0x0000026D802A0000-memory.dmp

        Filesize

        64KB

      • memory/1704-53-0x0000026D80280000-0x0000026D80290000-memory.dmp

        Filesize

        64KB

      • memory/1704-114-0x0000026D80480000-0x0000026D80490000-memory.dmp

        Filesize

        64KB

      • memory/1704-59-0x0000026D80380000-0x0000026D80390000-memory.dmp

        Filesize

        64KB

      • memory/1704-62-0x0000026D80390000-0x0000026D803A0000-memory.dmp

        Filesize

        64KB

      • memory/1704-61-0x0000026D802D0000-0x0000026D802E0000-memory.dmp

        Filesize

        64KB

      • memory/1704-60-0x0000026D802C0000-0x0000026D802D0000-memory.dmp

        Filesize

        64KB

      • memory/1704-65-0x0000026D802E0000-0x0000026D802F0000-memory.dmp

        Filesize

        64KB

      • memory/1704-67-0x0000026D803B0000-0x0000026D803C0000-memory.dmp

        Filesize

        64KB

      • memory/1704-66-0x0000026D803A0000-0x0000026D803B0000-memory.dmp

        Filesize

        64KB

      • memory/1704-71-0x0000026D802F0000-0x0000026D80300000-memory.dmp

        Filesize

        64KB

      • memory/1704-73-0x0000026D803C0000-0x0000026D803D0000-memory.dmp

        Filesize

        64KB

      • memory/1704-72-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-77-0x0000026D803D0000-0x0000026D803E0000-memory.dmp

        Filesize

        64KB

      • memory/1704-76-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-75-0x0000026D80300000-0x0000026D80310000-memory.dmp

        Filesize

        64KB

      • memory/1704-80-0x0000026D80310000-0x0000026D80320000-memory.dmp

        Filesize

        64KB

      • memory/1704-81-0x0000026D803E0000-0x0000026D803F0000-memory.dmp

        Filesize

        64KB

      • memory/1704-87-0x0000026D80330000-0x0000026D80340000-memory.dmp

        Filesize

        64KB

      • memory/1704-91-0x0000026D80420000-0x0000026D80430000-memory.dmp

        Filesize

        64KB

      • memory/1704-90-0x0000026D80410000-0x0000026D80420000-memory.dmp

        Filesize

        64KB

      • memory/1704-100-0x0000026D80450000-0x0000026D80460000-memory.dmp

        Filesize

        64KB

      • memory/1704-99-0x0000026D80440000-0x0000026D80450000-memory.dmp

        Filesize

        64KB

      • memory/1704-98-0x0000026D80430000-0x0000026D80440000-memory.dmp

        Filesize

        64KB

      • memory/1704-97-0x0000026D80350000-0x0000026D80360000-memory.dmp

        Filesize

        64KB

      • memory/1704-96-0x0000026D80340000-0x0000026D80350000-memory.dmp

        Filesize

        64KB

      • memory/1704-89-0x0000026D80400000-0x0000026D80410000-memory.dmp

        Filesize

        64KB

      • memory/1704-107-0x0000026D80460000-0x0000026D80470000-memory.dmp

        Filesize

        64KB

      • memory/1704-106-0x0000026D80360000-0x0000026D80370000-memory.dmp

        Filesize

        64KB

      • memory/1704-105-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-88-0x0000026D803F0000-0x0000026D80400000-memory.dmp

        Filesize

        64KB

      • memory/1704-14-0x0000026D80270000-0x0000026D80280000-memory.dmp

        Filesize

        64KB

      • memory/1704-108-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-110-0x0000026D80370000-0x0000026D80380000-memory.dmp

        Filesize

        64KB

      • memory/1704-151-0x0000026D80460000-0x0000026D80470000-memory.dmp

        Filesize

        64KB

      • memory/1704-21-0x0000026D802B0000-0x0000026D802C0000-memory.dmp

        Filesize

        64KB

      • memory/1704-58-0x0000026D802B0000-0x0000026D802C0000-memory.dmp

        Filesize

        64KB

      • memory/1704-116-0x0000026D80390000-0x0000026D803A0000-memory.dmp

        Filesize

        64KB

      • memory/1704-117-0x0000026D80490000-0x0000026D804A0000-memory.dmp

        Filesize

        64KB

      • memory/1704-119-0x0000026D803A0000-0x0000026D803B0000-memory.dmp

        Filesize

        64KB

      • memory/1704-121-0x0000026D804A0000-0x0000026D804B0000-memory.dmp

        Filesize

        64KB

      • memory/1704-120-0x0000026D803B0000-0x0000026D803C0000-memory.dmp

        Filesize

        64KB

      • memory/1704-123-0x0000026D803C0000-0x0000026D803D0000-memory.dmp

        Filesize

        64KB

      • memory/1704-124-0x0000026D804B0000-0x0000026D804C0000-memory.dmp

        Filesize

        64KB

      • memory/1704-127-0x0000026D804C0000-0x0000026D804D0000-memory.dmp

        Filesize

        64KB

      • memory/1704-126-0x0000026D803D0000-0x0000026D803E0000-memory.dmp

        Filesize

        64KB

      • memory/1704-129-0x0000026D803E0000-0x0000026D803F0000-memory.dmp

        Filesize

        64KB

      • memory/1704-130-0x0000026D804D0000-0x0000026D804E0000-memory.dmp

        Filesize

        64KB

      • memory/1704-132-0x0000026D803F0000-0x0000026D80400000-memory.dmp

        Filesize

        64KB

      • memory/1704-136-0x0000026D804E0000-0x0000026D804F0000-memory.dmp

        Filesize

        64KB

      • memory/1704-135-0x0000026D80420000-0x0000026D80430000-memory.dmp

        Filesize

        64KB

      • memory/1704-134-0x0000026D80410000-0x0000026D80420000-memory.dmp

        Filesize

        64KB

      • memory/1704-133-0x0000026D80400000-0x0000026D80410000-memory.dmp

        Filesize

        64KB

      • memory/1704-137-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-139-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-148-0x0000026D804F0000-0x0000026D80500000-memory.dmp

        Filesize

        64KB

      • memory/1704-147-0x0000026D80450000-0x0000026D80460000-memory.dmp

        Filesize

        64KB

      • memory/1704-146-0x0000026D80440000-0x0000026D80450000-memory.dmp

        Filesize

        64KB

      • memory/1704-145-0x0000026D80430000-0x0000026D80440000-memory.dmp

        Filesize

        64KB

      • memory/1704-152-0x0000026D80500000-0x0000026D80510000-memory.dmp

        Filesize

        64KB

      • memory/1704-111-0x0000026D80470000-0x0000026D80480000-memory.dmp

        Filesize

        64KB

      • memory/1704-157-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-159-0x0000026D80470000-0x0000026D80480000-memory.dmp

        Filesize

        64KB

      • memory/1704-162-0x0000026DF4FA0000-0x0000026DF4FA1000-memory.dmp

        Filesize

        4KB

      • memory/1704-166-0x0000026D802A0000-0x0000026D802B0000-memory.dmp

        Filesize

        64KB

      • memory/1704-165-0x0000026D80290000-0x0000026D802A0000-memory.dmp

        Filesize

        64KB

      • memory/1704-164-0x0000026D80270000-0x0000026D80280000-memory.dmp

        Filesize

        64KB

      • memory/1704-163-0x0000026D80280000-0x0000026D80290000-memory.dmp

        Filesize

        64KB

      • memory/1704-167-0x0000026D80000000-0x0000026D80270000-memory.dmp

        Filesize

        2.4MB

      • memory/1704-169-0x0000026D802C0000-0x0000026D802D0000-memory.dmp

        Filesize

        64KB

      • memory/1704-182-0x0000026D80390000-0x0000026D803A0000-memory.dmp

        Filesize

        64KB

      • memory/1704-181-0x0000026D80370000-0x0000026D80380000-memory.dmp

        Filesize

        64KB

      • memory/1704-180-0x0000026D80360000-0x0000026D80370000-memory.dmp

        Filesize

        64KB

      • memory/1704-179-0x0000026D80350000-0x0000026D80360000-memory.dmp

        Filesize

        64KB

      • memory/1704-178-0x0000026D80340000-0x0000026D80350000-memory.dmp

        Filesize

        64KB

      • memory/1704-177-0x0000026D80330000-0x0000026D80340000-memory.dmp

        Filesize

        64KB

      • memory/1704-175-0x0000026D80320000-0x0000026D80330000-memory.dmp

        Filesize

        64KB

      • memory/1704-174-0x0000026D80310000-0x0000026D80320000-memory.dmp

        Filesize

        64KB

      • memory/1704-173-0x0000026D80300000-0x0000026D80310000-memory.dmp

        Filesize

        64KB

      • memory/1704-172-0x0000026D802F0000-0x0000026D80300000-memory.dmp

        Filesize

        64KB

      • memory/1704-113-0x0000026D80380000-0x0000026D80390000-memory.dmp

        Filesize

        64KB

      • memory/1704-171-0x0000026D802E0000-0x0000026D802F0000-memory.dmp

        Filesize

        64KB

      • memory/1704-170-0x0000026D802D0000-0x0000026D802E0000-memory.dmp

        Filesize

        64KB

      • memory/1704-168-0x0000026D802B0000-0x0000026D802C0000-memory.dmp

        Filesize

        64KB

      • memory/1704-2-0x0000026D80000000-0x0000026D80270000-memory.dmp

        Filesize

        2.4MB

      • memory/1704-18-0x0000026D80280000-0x0000026D80290000-memory.dmp

        Filesize

        64KB

      • memory/1704-19-0x0000026D80290000-0x0000026D802A0000-memory.dmp

        Filesize

        64KB

      • memory/1860-288-0x000001C3DC880000-0x000001C3DC881000-memory.dmp

        Filesize

        4KB

      • memory/1860-303-0x000001C3DC880000-0x000001C3DC881000-memory.dmp

        Filesize

        4KB

      • memory/4292-244-0x000001F361AE0000-0x000001F361AE1000-memory.dmp

        Filesize

        4KB