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:: DreamHack ๐Ÿšฉ/wargame - reverse

reversing | [CodeEngn] Malware L07

by EunBird 2022. 5. 30.

https://dreamhack.io/wargame/challenges/374/

 

[CodeEngn] Malware L07

๋‹ค์Œ์€ ์•…์„ฑ์ฝ”๋“œ Flow์˜ ์ผ๋ถ€๋ถ„์ด๋‹ค. ๋ถ„์„๊ฒฐ๊ณผ ์ด ์•…์„ฑ์ฝ”๋“œ๋Š” ํŠน์ • ์‚ฌ์ดํŠธ์— ์ ‘์†์„ ์‹œ๋„ ํ•˜๊ณ  ์žˆ๋Š”๋ฐ ์ ‘์†์ด ์•ˆ๋ ๊ฒฝ์šฐ ๋ช‡์ดˆ ๋‹จ์œ„๋กœ ์žฌ์ ‘์†์„ ํ•œ๋‹ค. ๋ช‡ms ๋‹จ์œ„๋กœ ์žฌ์ ‘์†์„ ํ•˜๋Š”๊ฐ€

dreamhack.io

 

 

๋‹ค์Œ์€ ์•…์„ฑ์ฝ”๋“œ Flow์˜ ์ผ๋ถ€๋ถ„์ด๋‹ค.
๋ถ„์„๊ฒฐ๊ณผ ์ด ์•…์„ฑ์ฝ”๋“œ๋Š” ํŠน์ • ์‚ฌ์ดํŠธ์— ์ ‘์†์„ ์‹œ๋„ ํ•˜๊ณ  ์žˆ๋Š”๋ฐ
์ ‘์†์ด ์•ˆ๋ ๊ฒฝ์šฐ ๋ช‡์ดˆ ๋‹จ์œ„๋กœ ์žฌ์ ‘์†์„ ํ•œ๋‹ค.
๋ช‡ms ๋‹จ์œ„๋กœ ์žฌ์ ‘์†์„ ํ•˜๋Š”๊ฐ€

 

 

๋ฌธ์ œ๋Š” ์œ„์™€ ๊ฐ™๋‹ค.

 

์ ‘์†์ด ์•ˆ๋  ๊ฒฝ์šฐ -> false๋กœ ์ด์–ด์ง€๋Š” ๋ถ€๋ถ„์„ ์ฐพ์•„๋ณผ ์ƒ๊ฐ์ธ๋ฐ

๋˜ํ•œ, ์žฌ์ ‘์† ์‚ฌ์ด์— ์‹œ๊ฐ„์„ ๋‘๋Š” ๊ฒƒ์„ ๋ณด๋‹ˆ sleep์„ ํ†ตํ•ด ๋ฉˆ์ท„๋‹ค๊ฐ€ ์ด์–ด์ง€๋Š” ๊ฒƒ์œผ๋กœ ๋ณด์ด๊ธฐ๋„ ํ•œ๋‹ค.

 

 

์ฝ”๋“œ๋“ค์„ ์‚ดํŽด๋ณด๋‹ค ๋ณด๋‹ˆ Sleep ๊ณผ 96000h ๋ผ๋Š” 16์ง„์ˆ˜ ์ˆซ์ž๊ฐ€ ๋ˆˆ์— ๋ˆ๋‹ค.

16์ง„์ˆ˜ 0x96000๋ฅผ 10์ง„์ˆ˜๋กœ ๋ฐ”๊พผ ๊ฐ’๋งŒํผ ์‰ฌ์—ˆ๋‹ค๊ฐ€ ์žฌ์ ‘์†์ด ์ด๋ฃจ์–ด์ง€๋Š” ๊ฒƒ์ด ์•„๋‹๊นŒ ๋ผ๋Š” ์ƒ๊ฐ์ด ๋“ ๋‹ค.

 

16์ง„์ˆ˜ 0x96000 ๋ฅผ 10์ง„์ˆ˜๋กœ ๋ฐ”๊พธ๋ฉด 614400 ์ด๋‹ค.

 

๋”ฐ๋ผ์„œ FLAG = 614400

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