CVE-2026-27142 identifies a cross-site scripting (XSS) vulnerability within the Go programming language's standard library, specifically in the html/template package responsible for safe HTML templating. The issue stems from improper escaping of URLs inserted into the content attribute of HTML meta tags when these tags include an http-equiv attribute set to "refresh". The meta refresh tag is commonly used to redirect or refresh web pages after a specified time interval. In this context, the URL following "url=" in the content attribute is not properly neutralized, allowing an attacker to inject malicious JavaScript code that executes in the victim's browser. This vulnerability is classified under CWE-79, indicating improper neutralization of input during web page generation. The Go team introduced a new GODEBUG environment variable, htmlmetacontenturlescape, which controls whether URLs in meta content attributes are escaped; setting this to 0 disables escaping, potentially increasing exposure. Affected versions include all Go releases up to 1.26.0-0. No public exploits have been reported yet, but the vulnerability could be leveraged in web applications that dynamically generate meta refresh tags using untrusted input. Since the vulnerability allows script execution in users' browsers, it can lead to session hijacking, credential theft, or other client-side attacks. The lack of a CVSS score means severity must be assessed based on impact and exploitability factors.

The primary impact of CVE-2026-27142 is the potential for cross-site scripting attacks, which can compromise the confidentiality and integrity of user data by executing arbitrary scripts in the context of trusted web applications. This can lead to session hijacking, theft of sensitive information such as cookies or credentials, defacement, or redirection to malicious sites. Since the vulnerability involves meta refresh tags, attackers might exploit automatic page redirects to inject malicious payloads without requiring user interaction beyond visiting a crafted page. Organizations using Go's html/template package to generate web pages with meta refresh tags that include URLs derived from user input are at risk. This can affect web services, APIs, and internal tools built with Go, especially those that dynamically generate HTML content. The vulnerability could undermine user trust and lead to regulatory or compliance issues if exploited. Although no known exploits exist currently, the ease of exploitation and the widespread use of Go in web development suggest a significant potential impact if left unmitigated.

To mitigate CVE-2026-27142, organizations should first upgrade to a Go version where this vulnerability is addressed once a patch is released. Until then, developers should avoid inserting untrusted user input into the content attribute of meta refresh tags. Review all templates and code paths generating meta refresh tags to ensure URLs are properly sanitized and escaped. Avoid disabling the htmlmetacontenturlescape escaping by setting it to 0 unless absolutely necessary and fully understood, as this increases risk. Implement strict input validation and output encoding for any data used in HTML meta tags. Consider replacing meta refresh redirects with safer alternatives like HTTP redirects or JavaScript-based navigation with proper sanitization. Conduct thorough code audits and penetration testing focusing on XSS vectors involving meta tags. Employ Content Security Policy (CSP) headers to restrict script execution and reduce the impact of potential XSS attacks. Monitor web application logs for unusual meta tag usage or injection attempts. Educate developers on secure templating practices and the risks of improper escaping in HTML generation.