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CVE-2025-27591 PoC — below 安全漏洞

Source
Associated Vulnerability
Title:below 安全漏洞 (CVE-2025-27591)
Description:A privilege escalation vulnerability existed in the Below service prior to v0.9.0 due to the creation of a world-writable directory at /var/log/below. This could have allowed local unprivileged users to escalate to root privileges through symlink attacks that manipulate files such as /etc/shadow.
Description
a C exploit for CVE-2025-27591, which allow an attacker to escalate privilege to root.
Readme
# CVE-2025-27591 

## description
Basically `below` tool allow for universal modification on its log file which lead to privilege escalation as root.


## details.
The log file created by `below` is world-writable, allowing any user to modify or replace it. 
An attacker can exploit this by creating a symbolic link from the log file to /etc/passwd.

If the attacker can trigger an error in `below` that logs arbitrary input, and crafts that input in 
the format of a valid /etc/passwd entry, they can inject a new root user into the system.

In order for the exploit to work the attacker should be able to execute the `below` command as it should be run
as `root` then the user must have `sudo` permission or a way to run it.

## Compiling. 
```bash
git clone https://github.com/Cythonic1/CVE-2025-27591
cd CVE-2025-27591
gcc -static -W -Wall main.c ./libcrypt.a -o exploit
```

## usage
```bash
./exploit <username> <password>
```

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