CVE-2023-24540 Overview
CVE-2023-24540 is a critical command injection vulnerability affecting Golang's html/template package. The vulnerability exists because not all valid JavaScript whitespace characters are considered to be whitespace during template sanitization. Templates containing whitespace characters outside of the character set \t\n\f\r\\u0020\\u2028\\u2029 in JavaScript contexts that also contain actions may not be properly sanitized during execution.
Critical Impact
This vulnerability enables attackers to bypass template sanitization controls, potentially leading to arbitrary script injection in applications using Go's html/template package for rendering user-controlled content in JavaScript contexts.
Affected Products
- Golang Go (multiple versions)
Discovery Timeline
- 2023-05-11 - CVE-2023-24540 published to NVD
- 2025-01-24 - Last updated in NVD database
Technical Details for CVE-2023-24540
Vulnerability Analysis
The vulnerability stems from an incomplete character set definition for JavaScript whitespace characters within Go's template sanitization logic. When the html/template package processes templates that embed actions within JavaScript contexts, it relies on identifying whitespace boundaries to properly sanitize potentially dangerous content.
However, the sanitization routine only recognizes a subset of valid JavaScript whitespace characters (\t, \n, \f, \r, \\u0020, \\u2028, \\u2029). JavaScript actually recognizes additional whitespace characters as defined in the ECMAScript specification. By using these unrecognized whitespace characters, an attacker can craft malicious template content that bypasses the sanitization process entirely.
This bypass can lead to the injection of arbitrary JavaScript code into web pages generated by affected Go applications, resulting in cross-site scripting (XSS) attacks or other script-based exploits.
Root Cause
The root cause is an input validation error in Go's html/template package where the whitespace character set used for parsing JavaScript contexts does not align with the complete set of whitespace characters defined in the ECMAScript specification. This character set mismatch creates a gap in the sanitization logic that can be exploited to inject unsanitized content.
Attack Vector
An attacker can exploit this vulnerability remotely over the network by providing specially crafted input to a Go web application that uses html/template for rendering content in JavaScript contexts. The attack requires no authentication or user interaction.
The exploitation involves embedding malicious JavaScript code separated by whitespace characters that are valid in JavaScript but not recognized by Go's template sanitizer. When the template is rendered, the sanitizer fails to properly escape or neutralize the malicious content because it doesn't recognize the unusual whitespace as a token boundary.
For technical details on the vulnerability mechanism, refer to the Go.dev Issue #59721 and the Go.dev Vulnerability Report GO-2023-1752.
Detection Methods for CVE-2023-24540
Indicators of Compromise
- Unusual Unicode whitespace characters (outside the standard set) appearing in application logs or request data
- JavaScript execution errors in browser consoles that may indicate malformed injected scripts
- Web application firewall alerts for XSS-like payloads containing non-standard whitespace sequences
- Unexpected JavaScript behavior in pages rendered by Go applications using html/template
Detection Strategies
- Deploy web application firewall (WAF) rules to detect and block requests containing suspicious Unicode whitespace characters in JavaScript contexts
- Monitor application logs for template rendering errors or unusual character encoding patterns
- Implement static code analysis to identify Go applications using html/template with user-controlled JavaScript contexts
- Use SentinelOne's Singularity platform to detect anomalous process behavior indicative of successful exploitation
Monitoring Recommendations
- Enable verbose logging for Go applications using html/template to capture template rendering details
- Monitor web server access logs for requests containing encoded Unicode whitespace characters
- Set up alerts for unexpected script execution patterns in client-side monitoring tools
- Review network traffic for responses containing suspicious JavaScript patterns from Go-based services
How to Mitigate CVE-2023-24540
Immediate Actions Required
- Update Golang to the latest patched version that addresses CVE-2023-24540
- Audit Go applications for usage of html/template with JavaScript contexts containing user-controlled data
- Implement additional input validation to strip or reject non-standard whitespace characters before template processing
- Consider using Content Security Policy (CSP) headers to mitigate potential XSS impact
Patch Information
The Go team has released patches to address this vulnerability. The fix expands the whitespace character set recognized during template sanitization to include all valid JavaScript whitespace characters.
For detailed patch information, see:
Organizations using NetApp products should also refer to NetApp Security Advisory ntap-20241115-0008.
Workarounds
- Avoid passing user-controlled input directly into JavaScript contexts within Go templates
- Implement strict input validation to filter out non-standard Unicode whitespace characters before template processing
- Use the text/template package instead of html/template for non-HTML output, with manual escaping
- Apply defense-in-depth measures such as CSP headers to limit the impact of any successful injection
# Check Go version and update
go version
# Update to latest patched Go version
go install golang.org/dl/go1.20.4@latest
go1.20.4 download
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
