CVE-2014-6393 in Express Web Framework
Summary
by MITRE
The Express web framework before 3.11 and 4.x before 4.5 for Node.js does not provide a charset field in HTTP Content-Type headers in 400 level responses, which might allow remote attackers to conduct cross-site scripting (XSS) attacks via characters in a non-standard encoding.
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Analysis
by VulDB Data Team • 11/05/2019
The vulnerability identified as CVE-2014-6393 affects the Express web framework versions prior to 3.11 and 4.x versions before 4.5 within Node.js environments. This security flaw stems from the framework's inconsistent handling of HTTP Content-Type headers in error responses, specifically those in the 400 level range. The absence of a proper charset field in these headers creates a potential attack vector that could be exploited by malicious actors to execute cross-site scripting attacks through the manipulation of character encodings.
The technical nature of this vulnerability lies in the framework's failure to explicitly define character encoding in Content-Type headers for error responses. When Express generates HTTP 400 level responses, it omits the charset parameter in the Content-Type header, which typically should include something like application/json; charset=utf-8 or text/html; charset=utf-8. This omission creates ambiguity in how browsers interpret the character encoding of the response content, particularly when error messages contain non-standard or user-supplied characters that might be interpreted differently depending on the browser's default encoding behavior.
The operational impact of this vulnerability extends beyond simple XSS exploitation, as it represents a broader category of encoding-related security issues that align with CWE-1004 - Sensitive Cookie Without 'HttpOnly' flag and CWE-79 - Cross-site Scripting. Attackers could potentially craft malicious inputs that when processed by the vulnerable Express framework would result in unexpected character encoding behavior, allowing them to inject malicious scripts that execute in the context of the victim's browser session. This vulnerability specifically enables attackers to bypass certain security mechanisms that rely on proper character encoding detection and interpretation.
The exploitation of this vulnerability requires an attacker to submit crafted input that would trigger a 400 level error response from the vulnerable Express application while ensuring that the error message contains characters that could be interpreted as malicious script content when the browser attempts to render the response with an incorrect or ambiguous encoding. This type of attack is categorized under the ATT&CK technique T1203 - Exploitation for Client Execution and demonstrates how seemingly minor configuration issues in web frameworks can create significant security implications. The vulnerability essentially provides an indirect path for attackers to perform XSS attacks by leveraging the framework's inconsistent handling of HTTP response headers and character encoding specifications.
Organizations using vulnerable versions of Express should immediately upgrade to patched versions that properly include charset specifications in all HTTP Content-Type headers, particularly for error responses. Additionally, implementing proper input validation and sanitization measures can help mitigate the potential impact of this vulnerability, though the most effective mitigation remains the application of the official security patches provided by the Express framework maintainers. The vulnerability highlights the importance of proper HTTP header management and consistent character encoding practices in web application security, aligning with security standards that emphasize the need for explicit encoding declarations in all web responses to prevent encoding-related security issues.