Which versions of Astro are affected by CVE-2025-55303?

Organizations using versions of astro should be aware of notable risk from CVE-2025-55303, a cross-site scripting vulnerability rated CVSS 6.9.. A patch is available.

Is there a public PoC exploit available for CVE-2025-55303?

Yes, a public proof-of-concept exploit is available for CVE-2025-55303. Prioritise patching immediately. EPSS: 0.2%.

How to fix or mitigate CVE-2025-55303?

Within 7 days: Identify affected systems running versions of astro and apply vendor patches promptly. Verify Content-Security-Policy and output encoding.

Astro CVE-2025-55303

Q: What is the CVSS score of CVE-2025-55303?

CVE-2025-55303 has a CVSS 4.0 base score of 6.9 (Medium). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.2%.

MEDIUM

Cross-site Scripting (XSS) (CWE-79)

2025-08-19 security-advisories@github.com

XSS Astro

6.9

CVSS 4.0 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

6.9 MEDIUM

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Analysis Generated

Mar 28, 2026 - 19:07 vuln.today

Patch released

Mar 28, 2026 - 19:07 nvd

Patch available

PoC Detected

Nov 25, 2025 - 14:31 vuln.today

Public exploit code

CVE Published

Aug 19, 2025 - 19:15 nvd

MEDIUM 6.9

DescriptionGitHub Advisory

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.

AnalysisAI

Astro is a web framework for content-driven websites. Rated medium severity (CVSS 6.9), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

Technical ContextAI

This vulnerability is classified as Cross-Site Scripting (XSS) (CWE-79), which allows attackers to inject malicious scripts into web pages viewed by other users. 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 include: Astro. Version information: before 5.13.2.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Sanitize all user input, use Content-Security-Policy headers, encode output contextually (HTML, JS, URL). Use frameworks with built-in XSS protection.