Comprehensive Technical Analysis of CVE-2025-67084

CVE ID: CVE-2025-67084 CVSS Score: 9.9 (Critical) Vulnerability Type: Arbitrary File Upload → Remote Code Execution (RCE) Affected Software: InvoicePlane (versions through 1.6.3)

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1. Vulnerability Assessment & Severity Evaluation

Vulnerability Overview

CVE-2025-67084 is a file upload vulnerability in InvoicePlane, an open-source invoicing application. The flaw allows authenticated attackers to upload malicious PHP files disguised as legitimate attachments, which can then be executed remotely, leading to Remote Code Execution (RCE).

Severity Justification (CVSS 9.9 - Critical)

The CVSS v3.1 scoring breakdown is as follows:

Metric	Score	Justification
Attack Vector (AV)	Network (N)	Exploitable remotely over HTTP/HTTPS.
Attack Complexity (AC)	Low (L)	No specialized conditions required; standard file upload functionality.
Privileges Required (PR)	Low (L)	Requires authenticated access (user-level credentials).
User Interaction (UI)	None (N)	No victim interaction needed post-exploitation.
Scope (S)	Changed (C)	Compromise affects the entire web application and underlying server.
Confidentiality (C)	High (H)	Full system compromise possible (RCE).
Integrity (I)	High (H)	Attacker can modify files, databases, and system configurations.
Availability (A)	High (H)	Potential for denial-of-service (DoS) or complete system takeover.

Key Factors Contributing to Critical Severity:

• RCE Capability: Direct execution of arbitrary code on the server.
• Low Privilege Requirement: Only authenticated access is needed (e.g., a compromised low-privilege user account).
• No User Interaction: Exploitation does not require victim action post-upload.
• High Impact: Full system compromise, data exfiltration, lateral movement, and persistence.

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2. Potential Attack Vectors & Exploitation Methods

Exploitation Workflow

1. Authentication Bypass (Optional):

   • If default credentials (admin:admin) or weak passwords are in use, attackers may gain initial access.
   • Alternatively, phishing or credential stuffing could provide valid credentials.

2. Malicious File Upload:

   • Attacker navigates to the file upload functionality (e.g., invoice attachments, client documents).
   • Uploads a PHP file (e.g., shell.php) disguised as a legitimate file (e.g., .jpg, .pdf).
     • Bypass Techniques:
       • MIME Type Spoofing: Modifying Content-Type headers to mimic allowed file types.
       • Double Extensions: Uploading shell.php.jpg (if the application does not properly validate extensions).
       • Null Byte Injection: Using %00 to truncate file extensions (e.g., shell.php%00.jpg).

3. File Execution:

   • The attacker accesses the uploaded file via its known path (e.g., /uploads/attachments/shell.php).
   • The PHP code executes server-side, granting the attacker a web shell with the privileges of the web server (e.g., www-data).

4. Post-Exploitation:

   • Privilege Escalation: Exploiting misconfigurations (e.g., sudo misconfigurations, kernel exploits).
   • Lateral Movement: Accessing databases, internal networks, or other services.
   • Persistence: Installing backdoors, cron jobs, or SSH keys.
   • Data Exfiltration: Stealing sensitive financial data, customer records, or credentials.

Proof-of-Concept (PoC) Exploit

A basic exploitation example:

# Step 1: Authenticate (if required)
curl -X POST "http://target/invoiceplane/sessions/login" \
     -d "email=attacker@example.com&password=weakpassword"

# Step 2: Upload malicious PHP file
curl -X POST "http://target/invoiceplane/upload" \
     -H "Cookie: ci_session=VALID_SESSION_ID" \
     -F "file=@shell.php;filename=shell.php.jpg" \
     -F "client_id=1"

# Step 3: Trigger RCE
curl "http://target/invoiceplane/uploads/attachments/shell.php?cmd=id"

Expected Output:

uid=33(www-data) gid=33(www-data) groups=33(www-data)

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3. Affected Systems & Software Versions

Vulnerable Software

• InvoicePlane versions ≤ 1.6.3 (all prior versions are assumed vulnerable unless patched).
• Dependencies:
  • PHP (versions not specified, but likely all supported versions).
  • Web servers (Apache, Nginx) with improper file execution permissions.

Attack Surface

• Self-hosted InvoicePlane instances (common in SMBs, freelancers, and small accounting firms).
• Cloud-hosted instances (if misconfigured or exposed to the internet).
• Internal networks where InvoicePlane is deployed as an intranet application.

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4. Recommended Mitigation Strategies

Immediate Actions

1. Apply Patches:

   • Upgrade to InvoicePlane 1.6.4 (or later) once a patch is released.
   • Monitor the official GitHub repository for updates.

2. Temporary Workarounds:

   • Disable File Uploads: If not critical, disable the feature via configuration.
   • Restrict File Extensions: Modify .htaccess or web server rules to block .php execution in upload directories:

     <FilesMatch "\.(php|php5|phtml)$">
         Deny from all
     </FilesMatch>
     

   • Implement File Type Validation:
     • Use server-side MIME type verification (not just client-side).
     • Restrict uploads to whitelisted extensions (e.g., .pdf, .jpg, .png).
     • Rename uploaded files to random strings (e.g., UUID.ext).

3. Network-Level Protections:

   • Web Application Firewall (WAF): Deploy rules to block PHP file uploads (e.g., ModSecurity OWASP CRS).
   • Isolate InvoicePlane: Place behind a reverse proxy with strict access controls.
   • Disable PHP Execution in Upload Directories:

     location ~* /uploads/.*\.php$ {
         deny all;
         return 403;
     }
     

4. Monitoring & Detection:

   • Log File Uploads: Track all uploads for suspicious activity (e.g., .php files).
   • Intrusion Detection Systems (IDS): Alert on unusual PHP execution in upload directories.
   • File Integrity Monitoring (FIM): Detect unauthorized changes to critical files.

Long-Term Hardening

• Principle of Least Privilege (PoLP):
  • Run the web server with minimal permissions (e.g., www-data with no shell access).
  • Restrict database and filesystem access.
• Regular Security Audits:
  • Conduct penetration testing and code reviews for file upload vulnerabilities.
  • Use static application security testing (SAST) tools (e.g., SonarQube, Semgrep).
• User Training:
  • Educate users on phishing risks and secure password practices.
  • Enforce multi-factor authentication (MFA) for administrative access.

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5. Impact on the Cybersecurity Landscape

Broader Implications

1. Targeted Attacks on SMBs:

   • InvoicePlane is widely used by small businesses, freelancers, and accounting firms, making it an attractive target for:
     • Ransomware groups (e.g., LockBit, BlackCat) seeking initial access.
     • Financial fraud actors (e.g., stealing invoices, payment details).
     • State-sponsored APTs (if the target is of strategic interest).

2. Supply Chain Risks:

   • If InvoicePlane is integrated with other financial or ERP systems (e.g., QuickBooks, Xero), compromise could lead to lateral movement into larger enterprise networks.

3. Exploitation in the Wild:

   • Zero-day Exploits: If no patch is available, attackers may develop weaponized exploits (e.g., Metasploit modules).
   • Automated Scanning: Shodan/Censys queries may reveal exposed instances for mass exploitation.

4. Regulatory & Compliance Risks:

   • GDPR/CCPA Violations: Unauthorized access to customer data could result in heavy fines.
   • PCI DSS Non-Compliance: If payment data is exposed, merchants may lose processing capabilities.

Historical Context

• Similar vulnerabilities have been exploited in other invoicing systems (e.g., CVE-2021-31856 in Dolibarr, CVE-2020-28870 in Invoice Ninja).
• Lessons Learned:
  • File upload vulnerabilities remain a top OWASP risk (A01:2021 – Broken Access Control).
  • Authentication is not enough – even low-privilege users can escalate to RCE.

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6. Technical Details for Security Professionals

Root Cause Analysis

The vulnerability stems from inadequate file upload validation in InvoicePlane’s codebase, specifically:

1. Lack of File Extension Whitelisting:
   • The application does not enforce strict file type restrictions, allowing .php files to be uploaded.
2. Insufficient MIME Type Verification:
   • Client-provided Content-Type headers are trusted without server-side validation.
3. Improper File Storage:
   • Uploaded files are stored in a web-accessible directory (e.g., /uploads/attachments/) with executable permissions.
4. No File Content Inspection:
   • The application does not scan uploaded files for malicious payloads (e.g., PHP code in .jpg files).

Code-Level Vulnerability (Hypothetical Example)

A vulnerable file upload handler in PHP might look like:

// Vulnerable code snippet (InvoicePlane <= 1.6.3)
if (isset($_FILES['file'])) {
    $target_dir = "uploads/attachments/";
    $target_file = $target_dir . basename($_FILES["file"]["name"]);
    move_uploaded_file($_FILES["file"]["tmp_name"], $target_file);
    // No extension/MIME validation, no renaming
}

Fix Example:

// Secure implementation
$allowed_extensions = ['pdf', 'jpg', 'png'];
$file_extension = strtolower(pathinfo($_FILES["file"]["name"], PATHINFO_EXTENSION));

if (!in_array($file_extension, $allowed_extensions)) {
    die("Error: Invalid file type.");
}

$target_file = $target_dir . uniqid() . '.' . $file_extension; // Random filename
move_uploaded_file($_FILES["file"]["tmp_name"], $target_file);

Exploitation Detection & Forensics

1. Indicators of Compromise (IoCs):

   • File System:
     • Unexpected .php files in /uploads/attachments/.
     • Suspicious filenames (e.g., shell.php, backdoor.php, cmd.php).
   • Logs:
     • Unusual POST requests to /upload with .php files.
     • Web server logs showing PHP execution in upload directories.
   • Network:
     • Outbound connections from the web server to attacker-controlled IPs.
     • DNS queries for known C2 domains.

2. Forensic Analysis:

   • Timeline Analysis: Check file creation/modification times for uploaded PHP files.
   • Memory Forensics: Use Volatility or Rekall to detect web shells in memory.
   • Database Analysis: Review users and sessions tables for unauthorized access.

3. YARA Rule for Detection:

rule InvoicePlane_RCE_Webshell {
    meta:
        description = "Detects common PHP web shells in InvoicePlane uploads"
        author = "Cybersecurity Analyst"
        reference = "CVE-2025-67084"
    strings:
        $php_eval = /eval\(.*\$_/
        $php_system = /system\(.*\$_/
        $php_exec = /exec\(.*\$_/
        $php_shell_exec = /shell_exec\(.*\$_/
    condition:
        any of them
}

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Conclusion & Recommendations

Key Takeaways

• CVE-2025-67084 is a critical RCE vulnerability with a CVSS 9.9 score, requiring immediate patching.
• Exploitation is trivial for authenticated attackers, making it a high-risk issue for organizations using InvoicePlane.
• Mitigation requires a multi-layered approach, including patching, WAF rules, and file upload restrictions.

Action Plan for Security Teams

Priority	Action Item	Owner	Timeline
Critical	Apply vendor patch (once available)	IT/Security Team	Within 24 hours
High	Implement WAF rules to block PHP uploads	Security Operations	Within 48 hours
High	Disable PHP execution in upload directories	DevOps/Web Admins	Within 48 hours
Medium	Conduct a security audit of all file upload functionalities	Security Team	Within 1 week
Medium	Enforce MFA for all administrative accounts	Identity Team	Within 1 week
Low	Monitor for exploitation attempts (SIEM alerts)	SOC Team	Ongoing

Final Thoughts

This vulnerability underscores the critical importance of secure file upload handling in web applications. Organizations must proactively audit their software for similar flaws and enforce defense-in-depth strategies to prevent RCE attacks. Given the high severity of CVE-2025-67084, immediate action is required to prevent potential breaches.

For further updates, monitor:

• InvoicePlane GitHub
• CISA Known Exploited Vulnerabilities Catalog
• NVD Entry for CVE-2025-67084