CVE-2026-54300

Description

## Summary `@astrojs/netlify` converts Astro `image.remotePatterns` into Netlify Image CDN `images.remote_images` regular expressions with broader semantics than Astro's canonical matcher. A single wildcard hostname such as `*.example.com` is converted to an optional subdomain regex, so the apex host matches. A single wildcard pathname such as `/ok/*` is converted without end anchoring, so deeper paths match by prefix. ## Technical details The Netlify adapter generates regex strings for Netlify Image CDN from `image.remotePatterns`. For `*.example.com`, it emits `([a-z0-9-]+\\.)?example\\.com`, which makes the subdomain optional. Astro's canonical helper requires exactly one subdomain and rejects the apex host. For `/ok/*`, the adapter emits a segment regex but does not anchor the end of the URL. Netlify's Image CDN implementation treats `images.remote_images` entries as JavaScript regular expressions and calls `.test(sourceImageUrl.href)`, so a URL such as `/ok/a/b.svg` matches the `/ok/a` prefix even though Astro's helper rejects it. The latest npm package `@astrojs/[email protected]` contains this conversion logic, and a minimal Astro build writes the broadened patterns into `.netlify/v1/config.json`. ## Reproduction 1. Create an Astro app using `[email protected]` and `@astrojs/[email protected]`. 2. Configure Netlify output and a restrictive image pattern, for example `remotePatterns: [{ protocol: 'http', hostname: '*.localhost', pathname: '/ok/*' }]`. 3. Build the app and observe that `.netlify/v1/config.json` contains `http://([a-z0-9-]+\\.)?localhost(:[0-9]+)?(\\/ok/[^/?#]+)/?([?][^#]*)?`. 4. Serve a canary SVG on `127.0.0.1:9001`. 5. Request `/.netlify/images?url=http%3A%2F%2Flocalhost%3A9001%2Fok%2Fa.svg&w=100`. Astro's helper rejects the apex `localhost` for `*.localhost`, but Netlify Image CDN accepts it and fetches the canary. 6. As a negative control, request `/.netlify/images?url=http%3A%2F%2Flocalhost%3A9001%2Fnope%2Fa.svg&w=100`. This returns `403 Forbidden: Remote image URL not allowed` and does not hit the canary. 7. Request `/.netlify/images?url=http%3A%2F%2Flocalhost%3A9001%2Fok%2Fa%2Fb.svg&w=100`. Astro's `/ok/*` helper rejects this deeper path, but Netlify Image CDN accepts it and fetches the canary. ## Impact Any Astro app deployed with `@astrojs/netlify` and a restrictive `image.remotePatterns` config can expose a wider image-fetch boundary than intended. Public requests to the Netlify Image CDN endpoint can fetch URLs that Astro's own matcher would reject, including apex hosts for `*.host` patterns and deeper paths for `/path/*` patterns. The practical impact depends on what the application intended to isolate behind the remote image allowlist, but it can disclose image-like resources from unintended hosts or paths behind the same configured remote origin family. ## Remediation Generate regexes that exactly match Astro's canonical `matchHostname` and `matchPathname` semantics, and anchor the full URL match before writing `images.remote_images`. In particular, `*.example.com` should require exactly one subdomain and should not match `example.com`, and `/ok/*` should match exactly one additional path segment and should not match `/ok/a/b`.