CVE-2026-73490 in Loofah
Summary
by MITRE • 08/12/2026
Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. Prior to 2.25.2, Loofah's HTML5 sanitizer applies its local-reference restriction only to the xlink:href attribute on SVG use and feImage elements, while browsers also accept the plain href attribute. A crafted sanitized SVG can therefore reference an arbitrary same-origin external document; use may render external SVG content containing scripts or other dangerous content, and feImage may load external images for tracking. Applications that sanitize user-supplied SVG with Loofah's default allowlist are affected. This issue is fixed in version 2.25.2.
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Analysis
by VulDB Data Team • 08/12/2026
The vulnerability in Loofah versions prior to 2.25.2 represents a critical security flaw in HTML5 sanitization that stems from an incomplete implementation of local-reference restrictions for SVG elements. This issue specifically affects the sanitization of SVG content through the default allowlist configuration, where the library fails to properly enforce security boundaries on external resource references. The flaw exists because Loofah only applies its restrictive logic to the xlink:href attribute on SVG use and feImage elements while neglecting to apply the same protection to the standard href attribute that browsers actually support. This inconsistency creates a vector for attackers to bypass intended security controls and access arbitrary same-origin external documents through crafted SVG content.
The technical implementation flaw manifests in how Loofah processes SVG attributes during sanitization, where it maintains an incomplete understanding of browser behavior regarding external resource loading. When users submit SVG content containing elements like use or feImage with href attributes pointing to external resources, the sanitizer fails to block these references despite having mechanisms in place for xlink:href. This discrepancy allows malicious actors to construct SVG documents that can load external content from the same origin, potentially including scripts or other dangerous materials that would normally be blocked by proper sanitization. The vulnerability specifically targets applications that rely on Loofah's default HTML5 sanitizer with its standard allowlist configuration, making it particularly concerning for web applications that process user-supplied SVG content.
The operational impact of this vulnerability extends beyond simple cross-site scripting concerns to encompass broader security implications for web applications processing SVG content. When attackers exploit this flaw, they can potentially load external SVG files containing malicious scripts or other dangerous content into the application's context, leveraging the same-origin policy to bypass traditional security boundaries. The feImage element presents particular risk as it can load external images for tracking purposes, enabling passive monitoring of user interactions and potentially revealing sensitive information about users' browsing behavior. Additionally, the use element can render external SVG content that may contain embedded scripts or other malicious constructs, creating a vector for more sophisticated attacks that could compromise application integrity and user data.
This vulnerability aligns with CWE-20, "Improper Input Validation," and CWE-154, "Use of Obsolete Function," as it represents both inadequate input sanitization and the use of outdated security enforcement mechanisms. From an ATT&CK framework perspective, this issue maps to T1203, "Exploitation for Client Execution," and T1068, "Exploitation for Privilege Escalation," as attackers can leverage the vulnerability to execute malicious code through SVG content processing. The fix implemented in version 2.25.2 addresses this by expanding the sanitizer's protection to include all relevant href attributes across SVG elements, ensuring consistent enforcement of same-origin restrictions. Organizations should immediately update to Loofah 2.25.2 or later versions and conduct thorough security reviews of applications that process user-supplied SVG content to identify potential exploitation vectors. Additionally, implementing additional layers of validation for SVG content, such as content security policy headers and sandboxing mechanisms, can provide further protection against similar vulnerabilities in other libraries or custom implementations.