Summary
A bug in the build process allows any unauthenticated user to read parts of the server source code.
Details
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.
https://github.com/withastro/astro/blob/176fe9f113fd912f9b61e848b00bbcfecd6d5c2c/packages/astro/src/core/build/static-build.ts#L139
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.
PoC
Here is one example of an affected open-source website:
https://creatorsgarten.org/pages/index.astro.mjs.map
The file can be saved and opened using https://evanw.github.io/source-map-visualization/ to reconstruct the source code.
The above accurately mirrors the source code as seen in the repository: https://github.com/creatorsgarten/creatorsgarten.org/blob/main/src/pages/index.astro
The above was found as the 4th result (and the first one on Astro 5.0+) when making the following search query on GitHub.com (search results link):
path:astro.config.mjs @sentry/astro
This vulnerability is the root cause of https://github.com/withastro/astro/issues/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.
Impact
All server-output (SSR) projects on Astro 5 versions v5.0.3 through v5.0.6 (inclusive), 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 (SSG) projects built using Astro 4 versions 4.16.17 or older, or Astro 5 versions 5.0.7 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.
- Network attack vector.
- Low attack complexity.
- No privileges required.
- No interaction required from an authorized user.
- Scope is limited to first party. Although the source code of closed-source third-party software may also be exposed.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
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.
Frequently Asked Questions
- What is CVE-2024-56159? CVE-2024-56159 is a high-severity security vulnerability in astro (npm), affecting versions <= 4.16.17. It is fixed in 4.16.18, 5.0.8.
- Which versions of astro are affected by CVE-2024-56159? astro (npm) versions <= 4.16.17 is affected.
- Is there a fix for CVE-2024-56159? Yes. CVE-2024-56159 is fixed in 4.16.18, 5.0.8. Upgrade to this version or later.
- Is CVE-2024-56159 exploitable, and should I be worried? Whether CVE-2024-56159 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2024-56159 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2024-56159?
- Upgrade
astroto 4.16.18 or later - Upgrade
astroto 5.0.8 or later
- Upgrade