CVE-2025-22872: HTML Tokenizer XSS Vulnerability

CVE-2025-22872 Overview

CVE-2025-22872 is an Input Validation Error vulnerability in the Go golang.org/x/net/html tokenizer package. The tokenizer incorrectly interprets tags with unquoted attribute values that end with a solidus character (/) as self-closing. This parsing inconsistency affects both direct Tokenizer usage and the Parse functions, potentially leading to DOM construction errors where content is placed in the wrong scope, particularly when processing foreign content within <math> or <svg> contexts.

Critical Impact
Applications using the Go HTML tokenizer to process untrusted HTML content containing foreign elements may experience incorrect DOM tree construction, potentially enabling XSS attacks or content injection in security-sensitive parsing scenarios.

Affected Products

Go golang.org/x/net/html package (versions prior to the security patch)
Applications using the Go HTML tokenizer for parsing untrusted content
Systems with NetApp products utilizing affected Go components

Discovery Timeline

April 16, 2025 - CVE-2025-22872 published to NVD
May 16, 2025 - Last updated in NVD database

Technical Details for CVE-2025-22872

Vulnerability Analysis

This vulnerability stems from a parsing ambiguity in how the Go HTML tokenizer handles attribute values. When an HTML tag contains an unquoted attribute value that ends with a forward slash (/), the tokenizer misinterprets the trailing slash as indicating a self-closing tag rather than being part of the attribute value itself.

This behavior creates a deviation from the HTML5 parsing specification. The impact is twofold: when using the Tokenizer directly, affected tags are incorrectly flagged as self-closing; when using the higher-level Parse functions, the DOM tree construction becomes corrupted. The vulnerability is particularly pronounced when parsing foreign content namespaces such as SVG and MathML, where self-closing tag semantics differ from standard HTML.

The attack requires network access and involves high complexity, as exploitation depends on specific HTML structures being processed through the vulnerable tokenizer in a security-sensitive context.

Root Cause

The root cause lies in the tokenizer's attribute parsing logic, which fails to correctly distinguish between a solidus character that is part of an unquoted attribute value versus one that indicates a self-closing tag. The HTML5 specification has specific rules for handling unquoted attribute values, and this implementation does not correctly account for all edge cases involving the solidus character.

Attack Vector

The attack vector is network-based, requiring an attacker to supply maliciously crafted HTML content to an application using the vulnerable tokenizer. The crafted HTML would include tags with unquoted attribute values ending in / within foreign content contexts like SVG or MathML. When this content is parsed, the incorrect DOM construction could allow attacker-controlled content to escape its intended scope, potentially leading to Cross-Site Scripting (XSS) if the parsed output is rendered in a browser context.

For example, content that should be contained within an SVG element might be placed outside of it due to the parsing error, allowing HTML content to execute in unexpected contexts.

Detection Methods for CVE-2025-22872

Indicators of Compromise

Unexpected HTML content appearing outside of <svg> or <math> elements in rendered pages
Application logs showing parsing anomalies or DOM construction warnings
User reports of visual rendering inconsistencies in pages containing SVG or MathML content

Detection Strategies

Review application dependencies for the golang.org/x/net/html package and verify the installed version
Implement automated scanning for Go module dependencies using go list -m all to identify vulnerable versions
Monitor Content Security Policy (CSP) violation reports that may indicate XSS attempts exploiting this vulnerability
Audit code paths that process untrusted HTML input, particularly those handling SVG or MathML content

Monitoring Recommendations

Enable detailed logging for HTML parsing operations in production environments
Implement input validation metrics to track malformed HTML patterns being submitted to your applications
Set up alerts for anomalous parsing behavior or increased error rates in HTML processing pipelines

How to Mitigate CVE-2025-22872

Immediate Actions Required

Update the golang.org/x/net/html package to the latest patched version immediately
Audit all applications using the Go HTML tokenizer for potential exposure to untrusted HTML input
Implement additional input sanitization for HTML content containing foreign elements
Consider using Content Security Policy headers to mitigate potential XSS exploitation

Patch Information

The Go security team has released a fix for this vulnerability. The patch is available through the standard Go module update process. For detailed information about the fix, refer to the Go.dev Change Log Entry and the Go.dev Vulnerability Report. NetApp has also published a security advisory for affected products.

To update to the patched version, run:

bash

go get -u golang.org/x/net/html

Workarounds

Sanitize or reject HTML input containing unquoted attribute values with trailing solidus characters before processing
Avoid processing untrusted HTML content containing <svg> or <math> foreign elements until the patch is applied
Implement output encoding and Content Security Policy headers to reduce XSS impact if exploitation occurs
Consider using alternative HTML parsing libraries with independent implementations as a temporary measure