- Description: An attacker identifies a server-side Handlebars template that directly embeds user-controlled data without sanitization. They craft malicious Handlebars expressions within user input fields. The server-side application processes this input, directly injecting the malicious expressions into the template. Handlebars then executes these expressions during template rendering, allowing the attacker to run arbitrary code on the server.
- Impact: Remote Code Execution (RCE) on the server, full server compromise, data breach, denial of service.
- Affected Handlebars.js Component:
Handlebars.compile(when used insecurely), Template Rendering Engine. - Risk Severity: Critical
- Mitigation Strategies:
- Never directly embed user-controlled data into raw Handlebars templates.
- Use parameterized templates and pass user data as context variables.
- Implement strict input validation and sanitization before template rendering.
- Consider sandboxed Handlebars environments for sensitive applications.
- Regular security audits and code reviews of template rendering logic.
- Description: An attacker finds a client-side Handlebars template where user-controlled data is used in the template context without proper escaping. They inject malicious JavaScript code within user input fields. When the client-side JavaScript renders the Handlebars template with this malicious input, the injected JavaScript code executes in the user's browser, leading to XSS.
- Impact: Cross-Site Scripting (XSS), session hijacking, cookie theft, redirection to malicious sites, website defacement, malware distribution.
- Affected Handlebars.js Component:
Handlebars.compile(when used client-side), Template Rendering Engine, Default HTML Escaping. - Risk Severity: High
- Mitigation Strategies:
- Always escape user-controlled data when rendering client-side templates.
- Utilize Handlebars' built-in HTML escaping
{{expression}}for user data. - Use context-aware escaping if necessary for different contexts (JavaScript, CSS).
- Implement Content Security Policy (CSP) to mitigate XSS impact.
- Use Subresource Integrity (SRI) for Handlebars.js and external libraries.
- Description: An attacker exploits a custom Handlebars helper function that is poorly implemented and executes system commands based on user-provided input. They craft input that, when processed by the vulnerable helper function, executes arbitrary commands on the server operating system.
- Impact: Remote Code Execution (RCE) on the server, full server compromise, data breach, denial of service.
- Affected Handlebars.js Component: Custom Helper Functions,
Handlebars.registerHelper. - Risk Severity: Critical
- Mitigation Strategies:
- Apply secure coding practices to all custom helper functions.
- Implement strict input validation and sanitization within helper functions.
- Adhere to the principle of least privilege for helper functions.
- Avoid executing external commands or system calls in helper functions if possible.
- Regularly review and audit custom helper function code.
- Description: An attacker exploits a custom Handlebars helper function that generates unsafe HTML or JavaScript output based on user-controlled input. When this helper is used in a template and rendered in the browser, the unsafe output leads to XSS vulnerabilities.
- Impact: Cross-Site Scripting (XSS), session hijacking, cookie theft, redirection to malicious sites, website defacement, malware distribution.
- Affected Handlebars.js Component: Custom Helper Functions,
Handlebars.registerHelper. - Risk Severity: High
- Mitigation Strategies:
- Ensure helper functions that generate HTML or JavaScript output properly escape user-controlled data.
- Use Handlebars' escaping mechanisms within helper functions when generating output.
- Review helper function output to ensure it is safe and does not introduce XSS.