CVE-2025-47911
📋 TL;DR
This vulnerability in Go's html.Parse function allows attackers to cause denial of service by providing specially crafted HTML content that triggers quadratic parsing complexity. Applications using golang.org/x/net/html for HTML parsing are affected, particularly web servers, proxies, or any service that processes untrusted HTML input.
💻 Affected Systems
- Go applications using golang.org/x/net/html package
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to CPU exhaustion from parsing malicious HTML, potentially affecting all users of the vulnerable application.
Likely Case
Degraded performance or temporary service disruption when processing attacker-controlled HTML content, requiring restart of affected services.
If Mitigated
Minimal impact with proper input validation and resource limits in place, though some performance degradation may still occur.
🎯 Exploit Status
Exploitation requires ability to submit HTML content to vulnerable application. No authentication needed if application accepts untrusted input.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to latest golang.org/x/net/html package
Vendor Advisory: https://groups.google.com/g/golang-announce/c/jnQcOYpiR2c
Restart Required: Yes
Instructions:
1. Update Go modules: go get golang.org/x/net@latest
2. Update imports in code
3. Rebuild and redeploy application
4. Restart affected services
🔧 Temporary Workarounds
Input size limiting
allLimit maximum size of HTML input to prevent resource exhaustion
Implement request size limits in web server configuration
Timeout implementation
allAdd parsing timeouts to prevent indefinite processing
Use context.WithTimeout for parsing operations
🧯 If You Can't Patch
- Implement strict input validation to reject suspicious HTML patterns
- Deploy rate limiting and WAF rules to block repeated malicious requests
🔍 How to Verify
Check if Vulnerable:
Check if application imports golang.org/x/net/html and uses html.Parse function on untrusted inputCheck Version:
go list -m golang.org/x/netVerify Fix Applied:
Verify updated package version and test with known malicious HTML samples📡 Detection & Monitoring
Log Indicators:
- High CPU usage spikes
- Long parsing times in application logs
- Increased error rates for HTML processing
Network Indicators:
- Repeated large HTML payloads to parsing endpoints
- Unusual traffic patterns to HTML processing services
SIEM Query:
source="application_logs" AND ("html.Parse" OR "parsing timeout") AND cpu_usage>90%