CVE-2026-30830 in defuddle
Summary
by MITRE • 03/07/2026
Defuddle cleans up HTML pages. Prior to version 0.9.0, the _findContentBySchemaText method in src/defuddle.ts interpolates image src and alt attributes directly into an HTML string without escaping. An attacker can use a " in the alt attribute to break out of the attribute context and inject event handler. This issue has been patched in version 0.9.0.
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Analysis
by VulDB Data Team • 03/12/2026
The vulnerability identified as CVE-2026-30830 affects the Defuddle HTML cleaning library, specifically targeting the _findContentBySchemaText method implementation in the src/defuddle.ts file. This flaw exists in versions prior to 090 and represents a classic cross-site scripting vulnerability that arises from improper input sanitization during HTML string construction. The vulnerability occurs when the library processes HTML content and attempts to clean or modify image elements by interpolating src and alt attribute values directly into HTML strings without appropriate escaping mechanisms. The security impact stems from the library's failure to properly validate and sanitize user-supplied content before incorporating it into dynamically generated HTML markup.
The technical exploitation of this vulnerability relies on the ability of an attacker to inject malicious content into the alt attribute of image elements. When an attacker supplies a double quote character within the alt attribute value, the interpolation process fails to escape this character, allowing the attacker to break out of the attribute context and inject arbitrary HTML or JavaScript code. This type of injection vulnerability is classified as a CWE-79 - Cross-Site Scripting, specifically manifesting as a DOM-based XSS attack since the malicious payload is executed in the browser context when the HTML string is rendered. The attack vector demonstrates a failure in proper HTML escaping and input validation practices that should be enforced during dynamic HTML generation.
The operational impact of this vulnerability extends beyond simple code injection, as it enables attackers to potentially execute malicious scripts in the context of the victim's browser session. This could lead to session hijacking, data theft, or redirection to malicious websites, particularly when the library processes user-generated content or content from untrusted sources. The vulnerability affects any application that relies on Defuddle for HTML cleaning and sanitization, making it a critical security concern for web applications that handle user input or process external HTML content. The issue represents a failure in the library's defense-in-depth approach, where proper input validation should occur before any interpolation or string concatenation operations.
Mitigation strategies for this vulnerability require immediate deployment of version 090 or later, which implements proper HTML escaping for attribute values during the interpolation process. Organizations should conduct thorough code reviews to identify any other instances where similar interpolation patterns might exist within their applications or third-party libraries. The fix should incorporate proper HTML escaping mechanisms such as using DOM APIs for attribute setting rather than string interpolation, or implementing comprehensive escaping functions that handle all special HTML characters. Additionally, implementing Content Security Policy headers and regular security testing can provide additional layers of protection against similar vulnerabilities. This remediation aligns with ATT&CK technique T1203 - Exploitation for Client Execution, emphasizing the importance of input validation and output encoding in preventing client-side code injection attacks.