Security Overview

The HTML library prioritizes security by design with multiple built-in protection layers.

Security Features

Input Size Limits

Default maximum input is 50MB to prevent memory exhaustion:

cfg := html.DefaultConfig()
cfg.MaxInputSize = 10 * 1024 * 1024 // Adjust to 10MB

DOM Depth Limits

Default maximum depth of 500 prevents recursive bomb attacks:

cfg.MaxDepth = 200 // Tighten the limit

Path Traversal Prevention

File operations automatically detect and block path traversal attempts (e.g., ../../../etc/passwd), recording them via the audit system.

Panic Recovery

All extraction operations include built-in panic recovery, returning ErrInternalPanic errors to ensure services don't crash from malicious input.

Processing Timeout

Configurable processing timeout prevents malicious HTML from causing infinite processing:

cfg.ProcessingTimeout = 10 * time.Second

Content Sanitization

Optional content sanitization removes potentially malicious tags and attributes:

cfg.EnableSanitization = true

Audit System

See Audit System for detailed audit configuration.

The audit system can record the following security events:

Event	Description
AuditEventBlockedTag	Blocked HTML tag
AuditEventBlockedAttr	Blocked attribute
AuditEventBlockedURL	Blocked URL
AuditEventInputViolation	Input size violation
AuditEventDepthViolation	DOM depth violation
AuditEventPathTraversal	Path traversal attempt
AuditEventTimeout	Processing timeout
AuditEventEncodingIssue	Encoding anomaly

High-Security Configuration

cfg := html.HighSecurityConfig()
// Automatically enables: reduced limits, shorter timeouts, full audit

Error Handling

All security violations return clear errors supporting errors.Is / errors.As matching:

result, err := html.Extract(data)
if err != nil {
    switch {
    case errors.Is(err, html.ErrInputTooLarge):
        // Log and reject
    case errors.Is(err, html.ErrMaxDepthExceeded):
        // Possibly maliciously crafted
    case errors.Is(err, html.ErrInternalPanic):
        // Panic recovery, check input
    }
}