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

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2025-08-19 · updated 2026-06-17
Weakness: CWE-79

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.

Affected products

withastro astro: before 4.16.18; from 5.0.0 before 5.13.2 — fixed in 4.16.18, 5.13.2

How to fix

Upgrade to a fixed version: withastro astro 4.16.18, 5.13.2. Check the vendor advisory for mitigations.

References

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