CVE-2025-61925

When running Astro in on-demand rendering mode using a adapter such as the node adapter it is possible to maliciously send an X-Forwarded-Host header that is reflected when using the recommended Astro.url property as there is no validation that the value is safe.

Details

Astro reflects the value in X-Forwarded-Host in output when using Astro.url without any validation.

It is common for web servers such as nginx to route requests via the Host header, and forward on other request headers. As such as malicious request can be sent with both a Host header and an X-Forwarded-Host header where the values do not match and the X-Forwarded-Host header is malicious. Astro will then return the malicious value.

This could result in any usages of the Astro.url value in code being manipulated by a request. For example if a user follows guidance and uses Astro.url for a canonical link the canonical link can be manipulated to another site. It is not impossible to imagine that the value could also be used as a login/registration or other form URL as well, resulting in potential redirecting of login credentials to a malicious party.

As this is a per-request attack vector the surface area would only be to the malicious user until one considers that having a caching proxy is a common setup, in which case any page which is cached could persist the malicious value for subsequent users.

Many other frameworks have an allowlist of domains to validate against, or do not have a case where the headers are reflected to avoid such issues.

PoC

• Check out the minimal Astro example found here: https://github.com/Chisnet/minimal_dynamic_astro_server
• nvm use
• yarn run build
• node ./dist/server/entry.mjs
• curl --location 'http://localhost:4321/' --header 'X-Forwarded-Host: www.evil.com' --header 'Host: www.example.com'
• Observe that the response reflects the malicious X-Forwarded-Host header

For the more advanced / dangerous attack vector deploy the application behind a caching proxy, e.g. Cloudflare, set a non-zero cache time, perform the above curl request a few times to establish a cache, then perform the request without the malicious headers and observe that the malicious data is persisted.

This could affect anyone using Astro in an on-demand/dynamic rendering mode behind a caching proxy.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2025-61925 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.14.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-61925? CVE-2025-61925 is a medium-severity improper input validation vulnerability in astro (npm), affecting versions < 5.14.3. It is fixed in 5.14.3. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2025-61925? CVE-2025-61925 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of astro are affected by CVE-2025-61925? astro (npm) versions < 5.14.3 is affected.
4. Is there a fix for CVE-2025-61925? Yes. CVE-2025-61925 is fixed in 5.14.3. Upgrade to this version or later.
5. Is CVE-2025-61925 exploitable, and should I be worried? Whether CVE-2025-61925 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
6. What actually determines whether CVE-2025-61925 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.
7. How do I fix CVE-2025-61925? Upgrade astro to 5.14.3 or later.