CVE-2023-4241 – CVE-2023-4241 is a vulnerability in the lol-htm... (How to Fix)

Q: What is the severity of CVE-2023-4241?

CVE-2023-4241 has a CVSS score of 7.5 (HIGH). CVE-2023-4241 is a vulnerability in the lol-html HTML parsing library that causes panics (crashes) when processing certain malicious HTML inputs. This affects any application using lol-html to process untrusted third-party HTML content, potentially leading to denial of service.

📋 TL;DR

CVE-2023-4241 is a vulnerability in the lol-html HTML parsing library that causes panics (crashes) when processing certain malicious HTML inputs. This affects any application using lol-html to process untrusted third-party HTML content, potentially leading to denial of service.

💻 Affected Systems

Products:

lol-html library
Applications using lol-html for HTML processing

Versions: All versions before 0.3.4

Operating Systems: All

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects applications that process arbitrary/untrusted HTML input using lol-html.

📦 What is this software?

Lol Html by Cloudflare

View all CVEs affecting Lol Html →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete application crash and denial of service when processing attacker-controlled HTML, potentially disrupting critical services.

🟠

Likely Case

Application instability and crashes when processing malformed or malicious HTML from untrusted sources.

🟢

If Mitigated

Limited impact with proper input validation and error handling, though crashes may still occur.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending malicious HTML to an application using vulnerable lol-html versions.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 0.3.4 and later

Vendor Advisory: https://github.com/cloudflare/lol-html/security/advisories/GHSA-c3x7-354f-4p2x

Restart Required: Yes

Instructions:

1. Update lol-html dependency to version 0.3.4 or later. 2. Rebuild and redeploy affected applications. 3. Restart services using the updated library.

🔧 Temporary Workarounds

Input validation and sanitization

all

Implement strict input validation and HTML sanitization before passing content to lol-html

Error handling wrapper

all

Wrap lol-html calls in try-catch blocks to handle panics gracefully

🧯 If You Can't Patch

Implement rate limiting and request filtering for HTML processing endpoints
Deploy application behind a WAF with HTML content inspection capabilities

🔍 How to Verify

Check if Vulnerable:

Check package.json or Cargo.toml for lol-html version <0.3.4

Check Version:

For Rust: cargo tree | grep lol-html; For Node.js: npm list lol-html

Verify Fix Applied:

Verify lol-html version is 0.3.4 or higher in dependencies

📡 Detection & Monitoring

Log Indicators:

Application crashes/panics when processing HTML
Error logs containing lol-html panic messages
Increased error rates on HTML processing endpoints

Network Indicators:

Unusual HTML payloads causing service disruption
Repeated requests with malformed HTML to processing endpoints

SIEM Query:

source="application.logs" AND ("panic" OR "crash") AND "lol-html"

📊 Metadata

CVE ID: CVE-2023-4241

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-20

Published: August 16, 2023

Last Updated: November 21, 2024

🔗 References

https://github.com/cloudflare/lol-html/security/advisories/GHSA-c3x7-354f-4p2x Vendor Advisory
https://github.com/cloudflare/lol-html/security/advisories/GHSA-c3x7-354f-4p2x Vendor Advisory

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

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