Astro Cloudflare CVE-2026-41321

Summary

The fetch() call for remote images in packages/integrations/cloudflare/src/utils/image-binding-transform.ts (line 28) uses the default redirect: 'follow' behavior. This allows the Cloudflare Worker to follow HTTP redirects to arbitrary URLs, bypassing the isRemoteAllowed() domain allowlist check which only validates the initial URL.

All three other image fetch paths in the codebase correctly use { redirect: 'manual' }. This is an incomplete fix for GHSA-qpr4-c339-7vq8.

Confirmed on HEAD.

Root Cause

image-binding-transform.ts line 28:

const content = await (isRemotePath(href) ? fetch(imageSrc) : assets.fetch(imageSrc));

Missing { redirect: 'manual' }. The three protected paths:

// image-passthrough-endpoint.ts:23 response = await fetch(href, { redirect: 'manual' });

// assets/endpoint/shared.ts:11 const res = await fetch(src, { redirect: 'manual' });

// assets/utils/remoteProbe.ts:53 const response = await fetch(url, { redirect: 'manual' });

PoC

Demonstrated with Node.js that fetch() without redirect: 'manual' follows 302 redirects to arbitrary destinations:

Server A (allowed domain) returns 302 → Server B (internal)

fetch('http://allowed:19741/img.jpg') → follows 302 → hits http://internal:19742/secret fetch('http://allowed:19741/img.jpg', {redirect:'manual'}) → returns 302, internal server NOT hit

Attack path: attacker finds an open redirect on an allowed domain, crafts /_image?href=https://allowed-cdn.com/redirect?url=http://internal-service/, and the Worker follows the redirect to the unauthorized destination.

Impact

Bypasses the image.domains and image.remotePatterns allowlist for the default Cloudflare image service (cloudflare-binding). Enables blind SSRF to domains not in the allowlist. Same vulnerability class as GHSA-qpr4-c339-7vq8 (HIGH) which fixed the passthrough endpoint but missed this one.

Suggested Fix

const content = await (isRemotePath(href) ? fetch(imageSrc, { redirect: 'manual' }) : assets.fetch(imageSrc));