CVE-2025-64757

Executive Summary

CVE-2025-64757 is a path traversal vulnerability in the Astro web framework's development server, specifically within the image optimization endpoint. This flaw allows an unauthenticated remote attacker to read arbitrary image files from the host filesystem accessible to the Node.js process. The vulnerability is rated with a CVSS score of 3.5 (Low), but its impact is amplified in development environments where sensitive configuration files or private images may be exposed. The issue has been patched in Astro version 5.14.3.

Supply Chain & Package Security

Astro is distributed via the npm registry. This vulnerability affects the development server component, which is a core part of the astro package. Users relying on Astro for static site generation or server-side rendering are at risk if they expose the development server to untrusted networks. The package is widely used in the Jamstack ecosystem, and supply chain risk is mitigated by the availability of a patched version.

CVSS Breakdown & Threat Level

• CVSS Score: 3.5 (Low)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: Low (limited to image files)
• Integrity Impact: None
• Availability Impact: None

Threat Level: Low. The vulnerability is limited to reading image files and requires the development server to be exposed. However, in CI/CD pipelines or shared development environments, this could lead to leakage of sensitive assets.

Deep Dive & Mechanics

The vulnerability resides in the image optimization endpoint of Astro's development server. This endpoint is designed to serve optimized versions of images (e.g., resized, compressed) on-the-fly. The flaw occurs due to insufficient validation of the file path parameter provided by the client.

Root Cause: The endpoint accepts a path parameter that is used to construct a filesystem path without proper sanitization. An attacker can supply a path containing directory traversal sequences (e.g., ../) to escape the intended image directory and read arbitrary files.

Attack Flow:

1. The attacker sends a crafted HTTP request to the development server, targeting the image optimization endpoint.
2. The request includes a path parameter with traversal sequences, e.g., ?path=../../../../etc/passwd.
3. The server resolves the path relative to the image cache directory but fails to check if the final path is within the allowed scope.
4. The server reads the file and returns it as an image (or with an image MIME type), potentially exposing sensitive data.

Affected Component: packages/astro/src/vite-plugin-astro-server/image-endpoint.ts (or similar).

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Vulnerable endpoint handler
app.get('/_image', (req, res) => {
  const filePath = path.join(imageCacheDir, req.query.path);
  // No validation of filePath against allowed directory
  res.sendFile(filePath);
});

Patched Code (Conceptual):

// Patched endpoint handler
app.get('/_image', (req, res) => {
  const requestedPath = path.normalize(req.query.path);
  const fullPath = path.join(imageCacheDir, requestedPath);
  // Ensure the resolved path is within the allowed directory
  if (!fullPath.startsWith(imageCacheDir)) {
    return res.status(403).send('Forbidden');
  }
  res.sendFile(fullPath);
});

The patch adds a check to verify that the resolved absolute path starts with the intended image cache directory, preventing traversal outside the allowed scope.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A running Astro development server (version < 5.14.3) exposed on the network.
• Knowledge of the image optimization endpoint (typically /_image).

Exploitation Steps:

1. Identify the Astro development server (e.g., via Shodan or local network scanning).
2. Send a crafted request to read sensitive files:

   curl "http://target:4321/_image?path=../../../../etc/passwd"
   

3. If the server returns the file content (even as a broken image), the vulnerability is confirmed.
4. For more targeted attacks, attempt to read configuration files or private keys:

   curl "http://target:4321/_image?path=../../../../app/config.js"
   

Note: The server may only return files that are valid images or have image-like extensions. However, the underlying read operation can still leak binary data.

Blue Team

Detection:

• Monitor HTTP requests to the /_image endpoint for unusual path parameters containing ../ or absolute paths.
• Alert on repeated 403 errors from the patched server (indicating attempted exploitation).
• Use the detection rules provided below.

Honeypot:

• Deploy a fake Astro development server and log all requests to /_image for analysis.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests to /_image with path parameter containing ../ or / at the start.
  • Unusual file extensions in the response (e.g., .js, .json, .env).
• File System IOCs:
  • Unexpected access to files outside the image cache directory (e.g., /etc/passwd, .env).
• Log IOCs:
  • Server logs showing GET /_image?path=../../ entries.

Detection Engineering

YARA Rule

rule CVE_2025_64757_Astro_PathTraversal {
    meta:
        description = "Detects path traversal attempts against Astro image endpoint"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-64757"
    strings:
        $traversal1 = "../"
        $traversal2 = "..\\"
        $endpoint = "/_image"
    condition:
        $endpoint and (#traversal1 > 0 or #traversal2 > 0)
}

Sigma Rule

title: Astro Image Endpoint Path Traversal Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2025-64757 by accessing the /_image endpoint with path traversal sequences.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-64757
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: astro
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem: '/_image'
        cs-uri-query|contains: '../'
    condition: selection
falsepositives:
    - Legitimate use of relative paths in development (unlikely)
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-64757 Astro Image Endpoint Path Traversal"; flow:to_server,established; content:"/_image"; http_uri; content:"../"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Astro: Update to version 5.14.3 or later.

   npm install astro@latest
   

2. Restrict Network Access: Ensure the development server is not exposed to untrusted networks (e.g., use --host 127.0.0.1).
3. Firewall Rules: Block external access to port 4321 (default Astro dev server port) unless necessary.

Long-Term Mitigations:

• Implement input validation for all file path parameters in custom endpoints.
• Use a reverse proxy (e.g., Nginx) to add an additional layer of path validation.
• Regularly audit dependencies for known vulnerabilities using tools like npm audit.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.