前言

繼續ctf的旅程
攻防世界Misc高手進階區的5分題
本篇是picture2的writeup

發現攻防世界的題目分數是動態的
就僅以做題時的分數為準了

解題過程

給了個png

扔進stegsolve
無果

扔進winhex

看檔案頭FFD8FF發現是jpg檔案

看檔案尾FFD9後面還有內容

foremost分離
失敗

binwalk

匯出

開啟得到一串base64

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

解碼

發現應該是個檔案
而且開頭KP
可能是PK的混淆

指令碼儲存檔案

import base64

t = "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"
a = base64.b64decode(t)
with open('a', "bw") as f:
    f.write(a)
    f.close()

然後修改檔案頭

解壓發現要密碼
右邊給了提示

這裡的報錯資訊是integer division or modulo by zero

解壓得到code檔案
扔進winhex

這是UUencode

得到flag

結語

知識點

• 檔案頭
• base64轉檔案
• binwalk
• UUencode