CVE-2020-35217
📋 TL;DR
CVE-2020-35217 is a critical CSRF vulnerability in Vert.x-Web framework where CSRF verification incorrectly compares tokens within the session instead of validating request tokens against cookie tokens. This allows attackers to perform CSRF attacks without providing any CSRF token in requests, potentially enabling unauthorized actions on behalf of authenticated users. All applications using affected Vert.x-Web versions with CSRF protection enabled are vulnerable.
💻 Affected Systems
- Vert.x-Web framework
📦 What is this software?
Vert.x Web by Eclipse
Vert.x Web by Eclipse
Vert.x Web by Eclipse
Vert.x Web by Eclipse
⚠️ Risk & Real-World Impact
Worst Case
Attackers can perform any authenticated action on behalf of victims, including account takeover, data theft, financial transactions, or administrative operations depending on application functionality.
Likely Case
Unauthorized state-changing actions such as changing user settings, making purchases, or modifying data through authenticated endpoints.
If Mitigated
If proper CSRF controls are implemented correctly, impact is limited to applications with additional authentication bypass vulnerabilities.
🎯 Exploit Status
Exploitation requires the victim to be authenticated and visit a malicious site. The vulnerability is simple to exploit with basic web development knowledge.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Vert.x-Web 4.0.0-milestone5 and later
Vendor Advisory: https://github.com/vert-x3/vertx-web/pull/1613
Restart Required: Yes
Instructions:
1. Update Vert.x-Web dependency to version 4.0.0-milestone5 or later. 2. Update pom.xml or build.gradle with new version. 3. Rebuild and redeploy application. 4. Restart application server.
🔧 Temporary Workarounds
Disable CSRF Protection
allTemporarily disable CSRF protection until patching is possible. This removes the broken CSRF verification but leaves applications vulnerable to CSRF attacks.
Remove or comment out CSRFHandler configuration in your Vert.x application
Implement Custom CSRF Validation
allCreate custom middleware that properly validates CSRF tokens by comparing request tokens with cookie tokens.
Implement custom handler that validates 'X-CSRF-Token' header against CSRF cookie value
🧯 If You Can't Patch
- Implement additional authentication requirements for sensitive actions (MFA, re-authentication)
- Use SameSite=Strict cookie attribute and implement CORS restrictions
🔍 How to Verify
Check if Vulnerable:
Check if using Vert.x-Web version 4.0.0-milestone1 through milestone4 with CSRFHandler enabled. Review application dependencies and configuration.Check Version:
Check build configuration files: For Maven: grep -r 'vertx-web' pom.xml; For Gradle: grep -r 'vertx-web' build.gradleVerify Fix Applied:
Verify Vert.x-Web version is 4.0.0-milestone5 or later. Test CSRF protection by attempting to submit a form without proper CSRF token - should be rejected.📡 Detection & Monitoring
Log Indicators:
- Multiple successful state-changing requests from same IP with missing or mismatched CSRF tokens
- Unexpected successful POST/PUT/DELETE requests without proper CSRF validation logs
Network Indicators:
- Cross-origin requests to authenticated endpoints without proper CSRF tokens
- Requests from unexpected referrers to state-changing endpoints
SIEM Query:
web_requests method=POST status=200 csrf_token=null OR web_requests method=POST status=200 referer NOT IN allowed_domains