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:

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

# Update Go dependencies to latest patched versions
go get -u golang.org/x/net@latest
go mod tidy
go mod verify