@astrojs/node's trailing slash handling causes open redirect issue

Vulnerability Description

Astro is a web framework for content-driven websites. Following CVE-2025-54793 there's still an Open Redirect vulnerability in a subset of Astro deployment scenarios prior to version 9.4.1. Astro 5.12.8 addressed CVE-2025-54793 where https://example.com//astro.build/press would redirect to the external origin //astro.build/press. However, with the Node deployment adapter in standalone mode and trailingSlash set to "always" in the Astro configuration, https://example.com//astro.build/press still redirects to //astro.build/press. This affects any user who clicks on a specially crafted link pointing to the affected domain. Since the domain appears legitimate, victims may be tricked into trusting the redirected page, leading to possible credential theft, malware distribution, or other phishing-related attacks. This issue has been patched in version 9.4.1.

References

• https://github.com/withastro/astro/security/advisories/GHSA-9x9c-ghc5-jhw9
• https://github.com/withastro/astro/commit/5fc3c599cacb0172cc7d8e1202a5f2e8685d7ef2