CVE-2016-10516 in Werkzeug
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the render_full function in debug/tbtools.py in the debugger in Pallets Werkzeug before 0.11.11 (as used in Pallets Flask and other products) allows remote attackers to inject arbitrary web script or HTML via a field that contains an exception message.
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Analysis
by VulDB Data Team • 01/04/2023
The CVE-2016-10516 vulnerability represents a critical cross-site scripting flaw within the Pallets Werkzeug framework's debugger component, specifically affecting versions prior to 0.11.11. This vulnerability exists in the render_full function located within the debug/tbtools.py file, which is part of Werkzeug's debugging infrastructure. The flaw allows remote attackers to execute malicious web scripts or HTML code through exception message fields, creating a significant security risk for applications that utilize Werkzeug's debugger functionality in production environments. The vulnerability directly impacts web applications built using Pallets Flask and other frameworks that depend on Werkzeug's debugging capabilities.
The technical implementation of this vulnerability stems from inadequate input sanitization within the debugger's rendering mechanism. When an exception occurs in a web application, the debugger captures the exception message and displays it in a user-facing interface through the render_full function. The flaw occurs because the system fails to properly escape or sanitize special characters within exception messages before rendering them in the HTML output. Attackers can exploit this by crafting malicious exception messages containing script tags or other HTML elements that get executed in the context of other users' browsers. This represents a classic XSS vulnerability where untrusted data flows from the application's exception handling mechanism directly into the browser without proper sanitization, violating fundamental security principles of input validation and output encoding.
The operational impact of CVE-2016-10516 extends beyond simple script execution, as it can enable sophisticated attack vectors including session hijacking, credential theft, and data exfiltration. When exploited, the vulnerability allows attackers to inject malicious JavaScript code that can access cookies, localStorage, and other browser-stored data, potentially compromising user sessions and sensitive information. The vulnerability is particularly dangerous in web applications where debug mode might be enabled in production environments, as it provides attackers with a direct path to execute arbitrary code in users' browsers. This type of vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws, and represents a significant weakness in the application's security architecture that could be leveraged for broader attacks within the application ecosystem.
Organizations affected by this vulnerability should immediately implement mitigation strategies focusing on both immediate remediation and long-term architectural improvements. The primary and most effective mitigation involves upgrading to Werkzeug version 0.11.11 or later, which includes proper input sanitization and output encoding mechanisms that prevent the injection of malicious content. Additionally, administrators should disable debug mode in production environments to prevent exposure of the vulnerable debugger component. Security teams should implement comprehensive input validation and output encoding practices throughout their applications, particularly in exception handling code paths. The vulnerability also highlights the importance of following ATT&CK framework principles related to defense in depth, where multiple layers of security controls should be implemented to prevent exploitation of similar vulnerabilities. Organizations should also consider implementing content security policies to further mitigate the impact of potential XSS attacks, and conduct regular security assessments to identify and remediate similar vulnerabilities in their software dependencies.