Your Security Operations Team, on AI

this is a CTF challenge. try to get the flag.

Tool call: list_files with args: {} succeeded

Tool call: sandbox_execute with args: {"command":"file /sandbox/re2"} succeeded

Execution output:

{"stdout": "/sandbox/re2: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=08fba98083e7c1f7171fd17c82befdfe1dcbcc82, stripped\n", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {"command":"strings -n 5 /sandbox/re2 | head"} succeeded

Execution output:

{"stdout": "/lib64/ld-linux-x86-64.so.2\nlibstdc++.so.6\n__gmon_start__\n_Jv_RegisterClasses\n_ITM_deregisterTMCloneTable\n_ITM_registerTMCloneTable\n_ZNSaIcED1Ev\n_ZNSt8ios_base4InitD1Ev\n__gxx_personality_v0\n_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEC1EPKcRKS3_\n", "stderr": "", "exit_code": 0}_

Tool call: open_ghidra_server with args: {"filepath":"/sandbox/re2"} succeeded

Tool call: list_strings with args: {"filepath":"/sandbox/re2","limit":2000} succeeded

Tool call: sandbox_execute with args: {"command":"/sandbox/re2"} succeeded

Execution output:

{"stdout": "", "stderr": "bash: line 1: /sandbox/re2: Permission denied\n", "exit_code": 126}

Tool call: sandbox_execute with args: {"command":"chmod +x /sandbox/re2"} succeeded

Execution output:

{"stdout": "", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {"command":"/sandbox/re2"} succeeded

Execution output:

{"stdout": "Usage: /sandbox/re2 flag\n", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {"command":"/sandbox/re2 TEST"} succeeded

Execution output:

{"stdout": "Better luck next time\n", "stderr": "", "exit_code": 0}

Tool call: list_methods with args: {"filepath":"/sandbox/re2"} succeeded

Tool call: decompile_function with args: {"filepath":"/sandbox/re2","name":"entry"} succeeded

Tool call: decompile_function with args: {"filepath":"/sandbox/re2","name":"FUN_00400b89"} succeeded

Tool call: decompile_function with args: {"filepath":"/sandbox/re2","name":"FUN_00400b56"} succeeded

Tool call: get_data_by_address with args: {"filepath":"/sandbox/re2","address":"0x6020a0"} succeeded

Tool call: get_data_by_address with args: {"filepath":"/sandbox/re2","address":"0x6020c0"} succeeded

Tool call: sandbox_execute with args: {"command":"xxd -g 1 -s 0x602090 -l 256 /sandbox/re2"} succeeded

Execution output:

{"stdout": "", "stderr": "", "exit_code": 0}

Tool call: decompile_function with args: {"filepath":"/sandbox/re2","name":"FUN_00400b73"} succeeded

Tool call: sandbox_execute with args: {} succeeded

Execution output:

{"stdout": "length 0\n[]\n", "stderr": "", "exit_code": 0}

Tool call: list_data_items with args: {"filepath":"/sandbox/re2","offset":0,"limit":200} succeeded

Tool call: sandbox_execute with args: {} succeeded

Execution output:

{"stdout": "0\n()\n", "stderr": "", "exit_code": 0}

Tool call: list_segments with args: {"filepath":"/sandbox/re2"} succeeded

Tool call: decompile_function with args: {"filepath":"/sandbox/re2","name":"FUN_00400d3d"} succeeded

Tool call: sandbox_execute with args: {"command":"xxd -g 1 -s 0x602080 -l 256 /sandbox/re2"} succeeded

Execution output:

{"stdout": "", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {"command":"readelf -S /sandbox/re2 | grep -n \".data\""} succeeded

Execution output:

{"stdout": "36: [15] .rodata PROGBITS 0000000000400e40 00000e40\n56: [25] .data PROGBITS 0000000000602080 00002080\n", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {"command":"xxd -g 1 -s 0x2080 -l 256 /sandbox/re2"} succeeded

Execution output:

{"stdout": "00002080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................\n00002090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................\n000020a0: 58 0e 40 00 00 00 00 00 00 00 00 00 00 00 00 00 X.@.............\n000020b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................\n000020c0: 24 00 00 00 00 00 00 00 05 00 00 00 36 00 00 00 $...........6...\n000020d0: 65 00 00 00 07 00 00 00 27 00 00 00 26 00 00 00 e.......'...&...\n000020e0: 2d 00 00 00 01 00 00 00 03 00 00 00 00 00 00 00 -...............\n000020f0: 0d 00 00 00 56 00 00 00 01 00 00 00 03 00 00 00 ....V...........\n00002100: 65 00 00 00 03 00 00 00 2d 00 00 00 16 00 00 00 e.......-.......\n00002110: 02 00 00 00 15 00 00 00 03 00 00 00 65 00 00 00 ............e...\n00002120: 00 00 00 00 29 00 00 00 44 00 00 00 44 00 00 00 ....)...D...D...\n00002130: 01 00 00 00 44 00 00 00 2b 00 00 00 47 43 43 3a ....D...+...GCC:\n00002140: 20 28 47 4e 55 29 20 36 2e 31 2e 31 20 32 30 31 (GNU) 6.1.1 201\n00002150: 36 30 37 32 31 20 28 52 65 64 20 48 61 74 20 36 60721 (Red Hat 6\n00002160: 2e 31 2e 31 2d 34 29 00 47 43 43 3a 20 28 47 4e .1.1-4).GCC: (GN\n00002170: 55 29 20 36 2e 32 2e 31 20 32 30 31 36 30 39 31 U) 6.2.1 2016091\n", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {} failed

Tool call: decompile_function with args: {"filepath":"/sandbox/re2","name":"FUN_00400d9a"} succeeded

Tool call: decompile_function with args: {"filepath":"/sandbox/re2","name":"FUN_00400d7a"} succeeded

Tool call: sandbox_execute with args: {} succeeded

Execution output:

{"stdout": "0 []\n", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {} succeeded

Inference stopped because of the step limit.

Execution output:

{"stdout": "[36, 0, 5, 54, 101, 7, 39, 38, 45, 1, 3, 0, 13, 86, 1, 3, 101, 3, 45, 22, 2, 21, 3, 101, 0, 41, 68, 68, 1, 68, 43, 977486663, 1313286176, 908077397, 825110830, 825242144, 842477622, 1378361393, 1210082405, 908096609, 825110830, 2700333, 977486663, 1313286176, 908077397, 825111086, 825242144, 825831478, 1378361398, 1210082405, 908096609, 825111086, 2699821, 1752378880, 1953657971, 771777121, 1702129257, 771780722, 1702129518, 1229078830, 1734439981, 1869491712, 1731093876, 1647211886, 1684826485, 6580525, 1970169646, 1935763502, 1680736360, 2037608057, 1680736365, 1953721977, 1731068018, 1982756206, 1769173605, 771780207, 779447911, 1936876918, 1601073001, 1915617394, 778136677, 7240036, 1818587694, 1819291233, 1764622452, 7629166, 2019914798, 1714290804, 6909545, 1685025326, 6386785, 1600677166, 1835102822, 1684561765, 1697513586, 1919311720, 6647137, 1667458862, 1668834655, 1601466469]\nlen 122\n", "stderr": "", "exit_code": 0}

yes

Tool call: sandbox_execute with args: {} failed

Tool call: sandbox_execute with args: {} succeeded

Execution output:

{"stdout": "rodata len 0\nflag_chars length 0\n\n", "stderr": "", "exit_code": 0}

Tool call: sandbox_execute with args: {} succeeded

Execution output:

{"stdout": "L3t_ME_T3ll_Y0u_S0m3th1ng_1mp0rtant_A_{FL4G}_W0nt_b3_3X4ctly_th4t_345y_t0_c4ptur3_H0wev3r_1T_w1ll_b3_C00l_1F_Y0u_g0t_1t\nlength 119\npointer 0x400e58\nflag ALEXCTF{W3_L0v3_C_W1th_CL45535}\n", "stderr": "", "exit_code": 0}

Flag: ALEXCTF{W3_L0v3_C_W1th_CL45535}

How it was found (quick summary):

The main routine (FUN_00400b89) iterates through the user-supplied string character-by-character and compares each byte to entries in an array located in .data (0x6020c0).
At 0x6020a0 there is a pointer to a long obfuscated message stored in .rodata (0x400e58…).
The integer array in .data actually stores indices into that .rodata string; assembling those indices builds the real flag.
Re-building with a short Python script produced: “ALEXCTF{W3_L0v3_C_W1th_CL45535}”.

Submitting that string satisfies the program and solves the challenge.

show me the script that gets the flag.

Tool call: createDocument with args: {"filename":"extract_flag.py","kind":"code"} succeeded

I've placed a Python script (extract_flag.py) in the artifact pane.
Run it in the same directory as the re2 binary and it will print the flag.

Please use sandbox_execute tool to run extract_flag.py.

Tool call: sandbox_execute with args: {} succeeded

Execution output:

{"stdout": "Flag: ALEXCTF{W3_L0v3_C_W1th_CL45535}\n", "stderr": "", "exit_code": 0}

The extraction script executed successfully and printed:

Flag: ALEXCTF{W3_L0v3_C_W1th_CL45535}

That’s the complete working proof-of-concept in Python.

can you explain the program logic?

Program overview (symbols are the autogenerated names Ghidra gave).

Entry → FUN_00400b89
• Checks argc. If it isn’t 2, prints “Usage …” and exits.
• Builds a C++ std::string from argv[1] and then iterates over it with the usual begin() / end() iterator helpers.
• local_68 holds the current iterator.
• local_1c is a simple position counter (0, 1, 2 …).
Hidden reference data in .data
• At virtual address 0x6020a0 there is an 8-byte pointer that points to .rodata address 0x400e58.
• Starting at 0x400e58 is the long innocuous-looking text:

L3t_ME_T3ll_Y0u_S0m3th1ng_1mp0rtant_A_{FL4G}_W0nt_b3_3X4ctly_th4t_345y_t0_c4ptur3_H0wev3r_1T_w1ll_b3_C00l_1F_Y0u_g0t_1t

• Immediately after the pointer, at 0x6020c0, is an array of 32-bit integers. Each word is an index into the text above. These indices spell the flag.
The per-character loop
Pseudocode for the core body:
• FUN_00400d3d receives two iterators, converts them to raw pointers (FUN_00400dac), and returns whether they differ (i.e., iter != end).
• FUN_00400d9a dereferences the iterator (*iter).
• FUN_00400d7a increments the iterator (++iter).
• FUN_00400b56 prints “Better luck next time” and exits on the first mismatch.
• After every character matches, the loop ends and FUN_00400b73 prints “You should have the flag by now”.
Why the flag isn’t stored directly
The flag bytes never exist in memory as a contiguous string. They have to be reconstructed runtime from the big text + the index table. Reverse engineering that table (or simply running the program with a correct input) reveals the flag.
Reconstructing the flag electrically
A short script:
which yields

ALEXCTF{W3_L0v3_C_W1th_CL45535}

Hence the program simply verifies that the single command-line argument equals this flag, character-by-character, using an indirection layer to avoid placing the flag plainly in the binary.