CVE-2025-55303: astro XSS — Exploit & Fix

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.

Is your site exposed to CVE-2025-55303?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

6.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

CWE-115 CWE-115

Affected Products

Vendor	Product	Versions
astro	astro	< 4.16.18
astro	astro	5.0.0 — 5.13.2

References

Advisories & Patches

https://github.com/withastro/astro/commit/4d16de7f95db5d1ec1ce88610d2a95e606e83820 https://github.com/withastro/astro/security/advisories/GHSA-xf8x-j4p2-f749 https://github.com/withastro/astro/security/advisories/GHSA-xf8x-j4p2-f749

Exploits

https://github.com/withastro/astro/security/advisories/GHSA-xf8x-j4p2-f749 https://github.com/withastro/astro/security/advisories/GHSA-xf8x-j4p2-f749

Frequently Asked Questions

What is CVE-2025-55303? +

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. It has a CVSS v3.1 base score of 6.1 (MEDIUM).

How severe is CVE-2025-55303? +

CVE-2025-55303 has a CVSS v3.1 score of 6.1 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-55303? +

CVE-2025-55303 affects products from astro, specifically: astro. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-55303? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-40282

WeGIA is a web manager for charitable institutions. In versions prior to 3.6.10, a Stored Cross-Site Scripting (XSS) vulnerability allows …

CVE-2026-3317

Reflected Cross-Site Scripting (XSS) vulnerability in Navigate Content Management System. The vulnerability is present in the '/blog' endpoint because user …

CVE-2025-10354

Cross-Site Scripting (XSS) vulnerability reflected in Semantic MediaWiki. This vulnerability allows an attacker to execute JavaScript code in the victim's …

CVE-2026-41456

Bludit CMS prior to commit 6732dde contains a reflected cross-site scripting vulnerability in the search plugin that allows unauthenticated attackers …

CVE-2026-40872

mailcow: dockerized is an open source groupware/email suite based on docker. In versions prior to 2026-03b, the admin dashboard's Autodiscover …

CVE-2026-40878

mailcow: dockerized is an open source groupware/email suite based on docker. In versions prior to 2026-03b, the mailcow web interface …

CVE-2025-55303