CVE-2026-121447 in svg-sanitizer
Summary
by MITRE • 11/03/2026
svg-sanitizer before 1.1.0 contains a cross-site scripting vulnerability that allows attackers to bypass sanitization by placing javascript: URLs in the animateTransform values attribute. Attackers can upload crafted SVG files whose animateTransform targets the href attribute, executing arbitrary JavaScript when Safari users click the link.
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified in svg-sanitizer versions prior to 1.1.0 represents a critical failure in input validation and sanitization logic for Scalable Vector Graphics content. This flaw specifically manifests as a cross-site scripting issue where the library fails to adequately filter or neutralize malicious payloads embedded within SVG attributes. The core technical deficiency lies in how the sanitizer processes the animateTransform element, particularly when it interacts with the href attribute of anchor elements. By allowing javascript: URLs to persist through the sanitization process via specific manipulation of animation values, the tool effectively bypasses its own security controls, permitting arbitrary code execution upon rendering by vulnerable clients.
From a technical perspective, the exploit relies on the interaction between SVG animation properties and HTML hyperlink attributes. An attacker crafts an SVG file where the animateTransform element is configured to target or influence the href attribute of a link. When this malicious SVG is rendered in a browser environment that supports these specific SVG features, such as Safari, the browser interprets the javascript: protocol within the animated value as executable code rather than static text. This mechanism allows an attacker to inject and execute arbitrary JavaScript commands directly into the context of the victim's session. The success of this attack depends on the user interacting with the content, typically by clicking a link that has been dynamically modified or triggered through the SVG animation sequence, thereby initiating the script execution within the browser's security sandbox.
The operational impact of this vulnerability is significant for any application that accepts and renders user-supplied SVG data without robust server-side sanitization prior to passing it to client-side libraries like svg-sanitizer. If an attacker can upload or inject such a crafted SVG file, they achieve remote code execution capabilities within the victim's browser context. This leads to potential account takeover through session hijacking, theft of sensitive cookies and local storage data, defacement of the web application interface, or redirection to phishing sites. The risk is particularly acute in environments where users are expected to view uploaded images or graphics, as it transforms a standard file upload feature into a vector for delivering malicious scripts that bypass traditional content security policies if not properly configured.
To mitigate this vulnerability, organizations must immediately upgrade svg-sanitizer to version 1.1.0 or later, which addresses the specific parsing logic flaws related to animateTransform and href attribute handling. In addition to updating dependencies, developers should implement defense-in-depth strategies by enforcing strict allow-lists for SVG tags and attributes on the server side before any client-side processing occurs. It is crucial to ensure that javascript: URLs are explicitly blocked in all contexts where they pose a security risk, including within animation targets. Furthermore, implementing Content Security Policy headers with appropriate script-src directives can help mitigate the impact of such cross-site scripting attempts by restricting the sources from which scripts can be executed, thereby reducing the effectiveness of any residual vulnerabilities in client-side libraries.
This vulnerability aligns with CWE-79, known as Improper Neutralization of Input During Web Page Generation commonly referred to as Cross-site Scripting, due to the injection and execution of malicious script code via user-controllable input. It also maps to MITRE ATT&CK technique T1059.007, which covers JavaScript under Command and Control or Execution categories, depending on whether the payload is used for initial access persistence or active exploitation within a session. Understanding these mappings helps security teams prioritize remediation efforts based on established industry standards for vulnerability classification and threat modeling.