GHSA-2pvr-wf23-7pc7 CVE-2026-54299
Astro: Host header SSRF in prerendered error page fetch
- Severity
- 7.5 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.33%
- Chance of exploitation in the next 30 days. Higher than 26.51% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
6.4.6- Upgrade astro to this version or later
Description
Summary
Astro SSR apps with prerendered error pages (/404 or /500 using export const prerender = true) fetch those pages over HTTP at runtime when an error occurs. The URL for this fetch is derived from request.url, which in turn gets its origin from the incoming Host header. When the Host header is not validated against allowedDomains, an attacker can point the fetch at an arbitrary host and read the response.
Who is affected
This affects SSR deployments that:
- Have a prerendered 404 or 500 page
- Use
createRequestFromNodeRequestfromastro/app/nodewithapp.render()without overridingprerenderedErrorPageFetch— this includes custom servers built on the public API and third-party adapters
Not affected:
@astrojs/node>= 9.5.4 (reads error pages from disk)@astrojs/cloudflare(uses the ASSETS binding)- The dev server (renders error pages in-process)
How it works
createRequestFromNodeRequest builds request.url from the raw Host / :authority header. The allowedDomains option is accepted but only gates X-Forwarded-For — it does not constrain the URL origin. (The public createRequest does fall back to localhost for unvalidated hosts; this internal builder did not.)
When app.render() encounters a 404 or 500 with a prerendered error route, default-handler.ts constructs the error page URL using the origin from request.url and fetches it via prerenderedErrorPageFetch, which defaults to global fetch. The response body is served to the client.
An attacker sends a request with Host: attacker-host:port, triggers an error (e.g., requesting a nonexistent path for a 404), and receives the response from the attacker-controlled host reflected back.
Remediation
The error page fetch origin is now validated against allowedDomains before use. When the host is validated, the original origin is preserved. Otherwise, it falls back to localhost. The fetch is also wrapped in a try/catch so that connection failures degrade gracefully to a plain error response.
Credit
5ud0 / Tarmo Technologies
Affected versions
npm
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
astro npm → 6.4.6
- npm
npm install astro@6.4.6- yarn
yarn add astro@6.4.6- pnpm
pnpm add astro@6.4.6
Severity breakdown
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- Low
- Availability
- None
Weakness
CWE-20: Improper Input Validation
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
How to prevent it
- Architecture and Design: Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses. [REF-1109] [REF-1110] [REF-1111]
- Architecture and Design: Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
- Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server. Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
- Implementation: When your application combines data from multiple sources, perform the validation after the sources have been combined. The individual data elements may pass the validation step but violate the intended restrictions after they have been combined.
- Implementation: Be especially careful to validate all input when invoking code that crosses language boundaries, such as from an interpreted language to native code. This could create an unexpected interaction between the language boundaries. Ensure that you are not violating any of the expectations of the language with which you are interfacing. For example, even though Java may not be susceptible to buffer overflows, providing a large argument in a call to native code might trigger an overflow.
- Implementation: Directly convert your input type into the expected data type, such as using a conversion function that translates a string into a number. After converting to the expected data type, ensure that the input's values fall within the expected range of allowable values and that multi-field consistencies are maintained.
- Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control. Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.
- Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.
CWE-918: Server-Side Request Forgery (SSRF)
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
References
Advisories
Packages
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-98hj-9722-w3j8 Astro: Reflected/Stored XSS via unescaped <script>/<style> tag content in JSX/MDX rendering | Medium | Also affects astro |
| GHSA-mpr7-6m5w-76rw Astro: Arbitrary CSS injection in Astro View Transitions | Low | Also affects astro |
| GHSA-26w7-cxv4-gfx2 Astro: Remote code execution through AVIF image optimization | Critical | Also affects astro |
| GHSA-376h-93r7-7g6f Astro: Authorization bypass from missing path-segment boundary check when stripping the configured base | Medium | Also affects astro |
| GHSA-8mv7-9c27-98vc Astro: composable `astro/hono` pipeline bypasses `security.checkOrigin` when `middleware()` is absent or misordered | Medium | Also affects astro |
| GHSA-f48w-9m4c-m7f5 Astro: XSS via unescaped spread attribute names in renderHTMLElement (incomplete fix for CVE-2026-54298) | Medium | Also affects astro |
| GHSA-7pw4-f3q4-r2p2 Astro: Cross-site scripting via unescaped transition:* directive values on hydrated islands | Low | Also affects astro |
| GHSA-4g3v-8h47-v7g6 Astro: Reflected XSS via unescaped View Transition animation properties | Medium | Also affects astro |
Credits: 5ud0er, cookesan
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