CVE-2025-55303 PoC — Unauthorized third-party images in Astro’s _image endpoint

Title:Unauthorized third-party images in Astro’s _image endpoint (CVE-2025-55303)
Description:Astro is a web framework for content-driven websites. In versions of astro before 5.13.2 and 4.16.18, the image optimization endpoint in projects deployed with on-demand rendering allows images from unauthorized third-party domains to be served. On-demand rendered sites built with Astro include an /_image endpoint which returns optimized versions of images. A bug in impacted versions of astro allows an attacker to bypass the third-party domain restrictions by using a protocol-relative URL as the image source, e.g. /_image?href=//example.com/image.png. This vulnerability is fixed in 5.13.2 and 4.16.18.

Astro < 5.13.2 and < 4.16.18 contains an information disclosure vulnerability caused by improper validation of protocol-relative URLs in the image optimization endpoint, letting attackers serve images from unauthorized third-party domains, exploit requires on-demand rendering deployment.

 id: CVE-2025-55303

info:
  name: Astro - Unauthorized Third-Party Image Access
  author: theamanraw

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