Astro, a web framework for content-driven websites, versions 1.0.0 through 4.0.18 improperly handle the source.title and enclosure.type fields in RSS feed XML templates by directly interpolating them without XML-character escaping. These fields are only validated as strings without restrictions on XML special characters. An attacker controlling these fields can inject arbitrary XML, breaking out of attributes or closing elements early, resulting in corrupted feed structure and injection of false metadata such as malicious links. This vulnerability is identified as CWE-91 (XML Injection) and has a CVSS 3.1 base score of 4.3 (medium severity). The vulnerability was fixed in version 4.0.19.

An attacker who can control the source.title or enclosure.type fields can inject arbitrary XML into the RSS feed generated by Astro, corrupting the feed structure and injecting false metadata. This can cause feed readers to misparse or display attacker-controlled content, potentially misleading users or redirecting them to malicious URLs. In server-side rendering mode, the poisoned feed is served to all subscribers on every request, amplifying the impact. There is no indication of confidentiality or availability impact. No known exploits in the wild have been reported.

This vulnerability is fixed in Astro version 4.0.19. Users should upgrade to version 4.0.19 or later to remediate this issue. Until upgrading, avoid using untrusted input in the source.title and enclosure.type fields or implement proper XML character escaping before interpolation. Patch status is not explicitly stated in the vendor advisory, but the fix is confirmed in version 4.0.19.