CVE-2026-59728

Name of the Vulnerable Software and Affected Versions Astro versions 1.0.0 through 4.0.18

Description In the @astrojs/rss package, specifically within packages/astro-rss/src/index.ts, the source.title and enclosure.type item fields are interpolated directly into XML template strings without proper XML-character escaping before being processed by fast-xml-parser. Because these fields are validated only as strings without restrictions on special characters, an attacker controlling these values can inject arbitrary XML into the generated RSS feed. For instance, using a double quote in enclosure.type allows breaking out of an attribute, while using </source> in source.title can close an element prematurely to inject additional nodes. This can lead to corrupted feed structures, the injection of false metadata such as malicious links, and cause feed readers to display attacker-controlled content. When operating in SSR (Server-Side Rendering) mode with output: 'server', the poisoned feed is served to all subscribers on every request.

Recommendations Update Astro to version 4.0.19. As a temporary mitigation, restrict or sanitize the input values used for the source.title and enclosure.type fields to ensure they do not contain XML special characters.