CVE-2026-59729 in Astro
Summary
by MITRE • 07/27/2026
Astro is a web framework for content-driven websites. Versions prior to 7.0.6 are vulnerable to XSS through unescaped spread attribute names in renderHTMLElement. The fix for CVE-2026-54298 (GHSA-jrpj-wcv7-9fh9) added an INVALID_ATTR_NAME_CHAR guard to addAttribute() so that spread-prop attribute names containing "' >/= or whitespace are dropped. A second attribute-rendering path, renderHTMLElement() in packages/astro/src/runtime/server/render/dom.ts, has its own inline attribute loop that does not go through addAttribute() and was not updated. It interpolates the attribute name unescaped and only escapes the value, so untrusted prop keys spread onto a native-HTMLElement-subclass component can still break out of the attribute context. This issue has been fixed in version 7.0.6.
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Analysis
by VulDB Data Team • 07/27/2026
The vulnerability in Astro web framework affects versions prior to 7.0.6 and represents a cross-site scripting weakness originating from improper handling of spread attribute names during HTML element rendering. This flaw specifically impacts the renderHTMLElement function which processes attributes for native HTML elements, creating an avenue for malicious code injection through unescaped attribute names. The vulnerability stems from inconsistent attribute validation logic where one code path properly sanitizes attribute names while another does not, allowing attackers to inject malicious content through spread properties that are passed to native HTML elements.
The technical implementation of this vulnerability occurs within the packages/astro/src/runtime/server/render/dom.ts file where the renderHTMLElement function contains a dedicated inline attribute loop that bypasses the established addAttribute() method. While CVE-2026-54298 addressed similar issues by introducing an INVALID_ATTR_NAME_CHAR guard in addAttribute() that drops attribute names containing characters like "' >/= or whitespace, this fix was not consistently applied to the renderHTMLElement function. The second rendering path processes attribute names through interpolation without proper escaping, while only escaping attribute values, creating a dangerous gap in security controls.
This vulnerability operates at the intersection of several cybersecurity domains and can be categorized under CWE-79 as Cross-Site Scripting, specifically manifesting as reflected XSS through improper input validation during HTML generation. The operational impact extends beyond simple code injection to potentially allow full compromise of user sessions, data theft, or redirection to malicious sites when users interact with affected content. Attackers can leverage this vulnerability by crafting spread properties with malicious attribute names that break out of the HTML attribute context, particularly targeting native HTML elements that are commonly used in web applications.
The ATT&CK framework categorizes this vulnerability under T1203 as Exploitation for Client Execution and potentially T1566 as Phishing with Social Engineering. The attack surface is particularly concerning because it affects content-driven websites where user-generated content or dynamic properties might be passed through spread operators to HTML elements, making the exploitation vector more accessible in typical web application scenarios.
Mitigation strategies should begin with immediate upgrade to Astro version 7.0.6 or later where the vulnerability has been properly addressed through consistent implementation of attribute name validation across all rendering paths. Organizations should also implement comprehensive input sanitization policies for any dynamic attributes passed to HTML elements, particularly when dealing with user-supplied data or content that might be spread into component properties. Security teams should conduct thorough code reviews focusing on attribute handling functions and establish automated testing procedures to verify proper escaping of attribute names in all rendering contexts, ensuring that similar issues do not reoccur in other parts of the application stack.