CVE-2020-4054
📋 TL;DR
This CVE describes a cross-site scripting (XSS) vulnerability in the RubyGem sanitize library. When using the 'relaxed' configuration or custom configurations allowing certain HTML elements, malicious content within math or svg elements may bypass sanitization. This affects Ruby applications using sanitize versions 3.0.0 through 5.2.0 for HTML sanitization.
💻 Affected Systems
- RubyGem sanitize
📦 What is this software?
Sanitize by Sanitize Project
⚠️ Risk & Real-World Impact
Worst Case
Full XSS compromise allowing attackers to execute arbitrary JavaScript in users' browsers, potentially leading to session hijacking, credential theft, or complete account takeover.
Likely Case
Limited XSS attacks targeting specific users through crafted input, potentially stealing session cookies or performing actions on behalf of authenticated users.
If Mitigated
No impact if proper input validation and output encoding are implemented alongside sanitize, or if vulnerable configurations are not used.
🎯 Exploit Status
Exploitation requires user input that gets processed through vulnerable sanitize configurations and rendered in a browser.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.2.1
Vendor Advisory: https://github.com/rgrove/sanitize/security/advisories/GHSA-p4x4-rw2p-8j8m
Restart Required: No
Instructions:
1. Update Gemfile to specify 'sanitize', '~> 5.2.1' 2. Run 'bundle update sanitize' 3. Test application functionality after update
🔧 Temporary Workarounds
Remove vulnerable configurations
allAvoid using 'relaxed' config or custom configs that allow the vulnerable elements listed in the advisory.
Implement additional input validation
allAdd server-side validation to reject or sanitize content containing math or svg elements before passing to sanitize.
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) headers to mitigate XSS impact
- Use WAF rules to block requests containing suspicious math/svg element patterns
🔍 How to Verify
Check if Vulnerable:
Check Gemfile.lock or run 'bundle show sanitize' to see installed version. If version is between 3.0.0 and 5.2.0 inclusive, check if using vulnerable configurations.Check Version:
bundle show sanitize | grep -o 'sanitize.*'Verify Fix Applied:
Confirm sanitize version is 5.2.1 or higher via 'bundle show sanitize' and test that math/svg elements in user input are properly sanitized.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests containing math/svg elements
- Error logs showing sanitization failures
Network Indicators:
- HTTP requests with crafted HTML payloads targeting input fields
SIEM Query:
source="application.log" AND ("math" OR "svg") AND ("POST" OR "PUT")🔗 References
- https://github.com/rgrove/sanitize/commit/a11498de9e283cd457b35ee252983662f7452aa9
- https://github.com/rgrove/sanitize/releases/tag/v5.2.1
- https://github.com/rgrove/sanitize/security/advisories/GHSA-p4x4-rw2p-8j8m
- https://usn.ubuntu.com/4543-1/
- https://www.debian.org/security/2020/dsa-4730
- https://github.com/rgrove/sanitize/commit/a11498de9e283cd457b35ee252983662f7452aa9
- https://github.com/rgrove/sanitize/releases/tag/v5.2.1
- https://github.com/rgrove/sanitize/security/advisories/GHSA-p4x4-rw2p-8j8m
- https://usn.ubuntu.com/4543-1/
- https://www.debian.org/security/2020/dsa-4730
