CVE-2025-58190: Golang x/net/html DoS Vulnerability

CVE-2025-58190 Overview

The html.Parse function in the golang.org/x/net/html package contains an infinite parsing loop vulnerability that can be exploited by providing specially crafted HTML content. When processing certain malicious inputs, the parser enters an unrecoverable infinite loop state, causing the application to hang indefinitely and leading to denial of service (DoS) conditions.

Critical Impact

Applications using the Go net/html package for HTML parsing are vulnerable to denial of service attacks when processing untrusted HTML content, potentially causing service outages and resource exhaustion.

Affected Products

• golang.org/x/net/html package (vulnerable versions)
• Go applications utilizing the html.Parse function for HTML processing
• Web crawlers, scrapers, and content processors built with Go

Discovery Timeline

• 2026-02-05 - CVE CVE-2025-58190 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2025-58190

Vulnerability Analysis

This vulnerability is classified as an Algorithmic Complexity Attack within the Denial of Service category. The html.Parse function in Go's extended networking library fails to properly handle certain malformed or malicious HTML structures, causing the parsing algorithm to enter an infinite loop state.

The vulnerability exists in the HTML tokenization and tree construction phases of the parser. When specific sequences of malformed HTML elements are encountered, the parser's state machine fails to advance properly, resulting in continuous processing of the same input without termination. This behavior consumes CPU resources indefinitely without producing output or throwing an error.

Applications that accept untrusted HTML content—such as web scrapers, email processors, content management systems, or any service that sanitizes or transforms HTML—are particularly at risk. An attacker can craft malicious HTML payloads designed to trigger the infinite loop condition, effectively causing the target application to become unresponsive.

Root Cause

The root cause lies in the HTML parsing state machine implementation within golang.org/x/net/html. Certain edge cases in the input handling logic create conditions where the parser fails to make forward progress through the input stream. The parsing loop continues indefinitely because the termination conditions are never satisfied when processing the specific malformed input patterns.

Attack Vector

An attacker can exploit this vulnerability by submitting specially crafted HTML content to any application that uses the vulnerable html.Parse function. The attack requires no authentication and can be delivered through any input vector that eventually gets processed by the HTML parser.

The malicious HTML content triggers the infinite loop during parsing, causing the goroutine handling the request to hang indefinitely. In server applications, repeated exploitation can exhaust the available goroutine pool or other system resources, leading to complete service unavailability.

For detailed technical information about the vulnerability mechanism, refer to the Go Vulnerability Advisory GO-2026-4441 and the associated code review.

Detection Methods for CVE-2025-58190

Indicators of Compromise

• Goroutines stuck in html.Parse operations that never complete
• Abnormally high CPU utilization by Go applications processing HTML content
• HTTP requests with unusually crafted HTML payloads targeting parsing endpoints
• Application timeout errors or unresponsive services following HTML content submission

Detection Strategies

• Monitor goroutine counts and CPU usage in Go applications that process HTML content
• Implement request timeout monitoring for HTML parsing operations
• Review application logs for parsing operations that exceed expected duration thresholds
• Deploy SentinelOne Singularity XDR to detect resource exhaustion patterns indicative of DoS attacks

Monitoring Recommendations

• Establish baseline metrics for HTML parsing operation duration and monitor for anomalies
• Configure alerting for goroutine count spikes in applications using golang.org/x/net/html
• Implement distributed tracing to identify parsing operations that fail to complete
• Monitor system resource utilization (CPU, memory) for Go services handling untrusted HTML

How to Mitigate CVE-2025-58190

Immediate Actions Required

• Update the golang.org/x/net/html package to the latest patched version immediately
• Audit applications to identify all usage of the html.Parse function with untrusted input
• Implement parsing timeouts using Go's context package with deadline or cancellation support
• Consider input validation or size limits on HTML content before parsing

Patch Information

The Go team has addressed this vulnerability through a code fix. Review the Go Code Review CL 709875 for patch details. Update your dependencies by running go get -u golang.org/x/net/html and rebuilding affected applications.

For official announcements and update instructions, refer to the GoLang Announce Post.

Workarounds

• Wrap all html.Parse calls with context timeouts to prevent indefinite hangs
• Implement input size limits to restrict the maximum HTML content size processed
• Run HTML parsing operations in isolated goroutines with proper timeout and cancellation handling
• Consider alternative HTML parsing libraries if immediate patching is not feasible

# Update golang.org/x/net to latest patched version
go get -u golang.org/x/net/html@latest

# Verify the installed version
go list -m golang.org/x/net

# Rebuild affected applications
go build -o myapp ./...