CVE-2024-56159 Server source code is exposed to the public if sourcemaps are enabled

What is CVE-2024-56159?

CVE-2024-56159 is a high-severity vulnerability in withastro astro, published on 19 Dec 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Astro is a web framework for content-driven websites. A bug in the build process allows any unauthenticated user to read parts of the server source code. During build, along with client assets such as css and font files, the sourcemap files **for the server code** are moved to a publicly-accessible folder. Any outside party can read them with an unauthorized HTTP GET request to the same server hosting the rest of the website. While some server files are hashed, making their access obscure, the files corresponding to the file system router (those in `src/pages`) are predictably named. For example. the sourcemap file for `src/pages/index.astro` gets named `dist/client/pages/index.astro.mjs.map`. This vulnerability is the root cause of issue #12703, which links to a simple stackblitz project demonstrating the vulnerability. Upon build, notice the contents of the `dist/client` (referred to as `config.build.client` in astro code) folder. All astro servers make the folder in question accessible to the public internet without any authentication. It contains `.map` files corresponding to the code that runs on the server. All **server-output** projects on Astro 5 versions **v5.0.3** through **v5.0.7**, that have **sourcemaps enabled**, either directly or through an add-on such as `sentry`, are affected. The fix for **server-output** projects was released in **[email protected]**. Additionally, all **static-output** projects built using Astro 4 versions **4.16.17 or older**, or Astro 5 versions **5.0.8 or older**, that have **sourcemaps enabled** are also affected. The fix for **static-output** projects was released in **[email protected]**, and backported to Astro v4 in **[email protected]**. The immediate impact is limited to source code. Any secrets or environment variables are not exposed unless they are present verbatim in the source code. There is no immediate loss of integrity within the the vulnerable server. However, it is possible to subsequently discover another vulnerability via the revealed source code . There is no immediate impact to availability of the vulnerable server. However, the presence of an unsafe regular expression, for example, can quickly be exploited to subsequently compromise the availability. The fix for **server-output** projects was released in **[email protected]**, and the fix for **static-output** projects was released in **[email protected]** and backported to Astro v4 in **[email protected]**. Users are advised to update immediately if they are using sourcemaps or an integration that enables sourcemaps.

Weakness: CWE-219

Which versions are affected by CVE-2024-56159?

4 open source packages ship an affected version, including astro. It affects 1 product.

Products include Astro Astro.

How do I fix CVE-2024-56159?

Upgrade astro to a fixed version for your release line: 4.16.18 or 5.0.8.

Is CVE-2024-56159 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2024-56159 exists.

Public exploit code: 1 Nuclei template.

Other vulnerabilities in withastro astro

• CVE-2026-54299 Astro: Host header SSRF in prerendered error page fetch High 7.5
• CVE-2025-59837 astro allows bypass of image proxy domain validation leading to SSRF and potential XSS High 7.2
• CVE-2026-50146 Astro: Reflected XSS via unescaped slot name High 7.1
• CVE-2025-64764 Astro is vulnerable to Reflected XSS via the server islands feature High 7.1
• CVE-2025-64765 Astro middleware authentication checks based on url.pathname can be bypassed via url encoded values Medium 6.9

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-49w6-73cw-chjr.