CVE-2026-79320 in stenciljs
Summary
by MITRE • 09/21/2026
Stencil core 4.43.5 contains a DOM-based cross-site scripting (XSS) vulnerability in the component runtime. When a downstream application enables the experimental slot fixes option and uses scoped components, assigning a string to the textContent property of such a component's host element causes the value to be parsed as HTML instead of being inserted as text. If an application writes attacker-controlled data to these host elements, the data can be interpreted as markup and script can execute in the context of the application's origin.
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Analysis
by VulDB Data Team • 09/21/2026
The vulnerability identified in Stencil core version 4.43.5 represents a significant security flaw within the component runtime architecture, specifically manifesting as a DOM-based cross-site scripting (XSS) issue. This defect arises from an incorrect handling of text content assignment when specific experimental features are enabled. The root cause lies in how the framework processes string assignments to the textContent property of host elements for scoped components under particular configuration conditions. Instead of treating the assigned value strictly as plain text, which is the expected behavior for security and data integrity, the runtime erroneously parses the input as HTML markup. This deviation from standard DOM manipulation protocols creates a direct pathway for malicious script injection if an application fails to properly sanitize user-supplied data before binding it to these specific component instances.
The operational impact of this vulnerability is severe because it allows attackers to execute arbitrary JavaScript code within the context of the victim's browser session and origin. When a downstream application enables the experimental slot fixes option, which modifies how slots are handled in scoped components, the security boundary provided by standard text insertion mechanisms is compromised. If an attacker can control any data that gets assigned to the textContent property of such a host element, they can inject malicious scripts. These scripts will execute with the privileges and permissions associated with the vulnerable application's origin. This capability enables a range of attacks including session hijacking through cookie theft, credential harvesting via form manipulation, defacement of the user interface, or using the compromised browser as a pivot point for further network intrusions against internal resources that trust the application's domain.
From a classification perspective, this vulnerability aligns with CWE-79, which describes Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. More specifically, it falls under DOM-based XSS where the vulnerability exists in client-side code rather than server-side processing. In terms of offensive security frameworks such as MITRE ATT&CK for Enterprise or Mobile, this technique corresponds to Client-Side Injection (T1059) and potentially Obfuscated Files or Information if the injected scripts are encoded to evade detection. The exploitation relies on the attacker's ability to influence data flow into a vulnerable DOM property, making it critical for developers to understand how framework-specific optimizations can inadvertently introduce security regressions when experimental features interact with standard web APIs in unexpected ways.
Mitigation strategies must address both immediate remediation and long-term architectural changes. The most effective solution is to upgrade the Stencil core library to a version where this parsing logic has been corrected, ensuring that textContent assignments are strictly treated as plain text regardless of other configuration settings. For applications unable to immediately update their dependencies, developers should implement rigorous input validation and output encoding on all data sources before they reach any component host elements. It is also advisable to disable the experimental slot fixes option if it is not strictly required for functionality, thereby reverting to a more stable and secure rendering path. Additionally, implementing Content Security Policy (CSP) headers can provide an additional layer of defense by restricting the sources from which scripts are allowed to execute, significantly reducing the impact even if an injection attempt succeeds. Regular security audits focusing on data binding practices within component-based frameworks are essential to prevent similar DOM manipulation vulnerabilities in future development cycles.