The SentinelOne Annual Threat Report - A Defenders Guide from the FrontlinesThe SentinelOne Annual Threat ReportGet the Report
Experiencing a Breach?Blog
Get StartedContact Us
SentinelOne
  • Platform
    Platform Overview
    • Singularity Platform
      Welcome to Integrated Enterprise Security
    • AI for Security
      Leading the Way in AI-Powered Security Solutions
    • Securing AI
      Accelerate AI Adoption with Secure AI Tools, Apps, and Agents.
    • How It Works
      The Singularity XDR Difference
    • Singularity Marketplace
      One-Click Integrations to Unlock the Power of XDR
    • Pricing & Packaging
      Comparisons and Guidance at a Glance
    Data & AI
    • Purple AI
      Accelerate SecOps with Generative AI
    • Singularity Hyperautomation
      Easily Automate Security Processes
    • AI-SIEM
      The AI SIEM for the Autonomous SOC
    • AI Data Pipelines
      Security Data Pipeline for AI SIEM and Data Optimization
    • Singularity Data Lake
      AI-Powered, Unified Data Lake
    • Singularity Data Lake for Log Analytics
      Seamlessly Ingest Data from On-Prem, Cloud or Hybrid Environments
    Endpoint Security
    • Singularity Endpoint
      Autonomous Prevention, Detection, and Response
    • Singularity XDR
      Native & Open Protection, Detection, and Response
    • Singularity RemoteOps Forensics
      Orchestrate Forensics at Scale
    • Singularity Threat Intelligence
      Comprehensive Adversary Intelligence
    • Singularity Vulnerability Management
      Application & OS Vulnerability Management
    • Singularity Identity
      Identity Threat Detection and Response
    Cloud Security
    • Singularity Cloud Security
      Block Attacks with an AI-Powered CNAPP
    • Singularity Cloud Native Security
      Secure Cloud and Development Resources
    • Singularity Cloud Workload Security
      Real-Time Cloud Workload Protection Platform
    • Singularity Cloud Data Security
      AI-Powered Threat Detection for Cloud Storage
    • Singularity Cloud Security Posture Management
      Detect and Remediate Cloud Misconfigurations
    Securing AI
    • Prompt Security
      Secure AI Tools Across Your Enterprise
  • Why SentinelOne?
    Why SentinelOne?
    • Why SentinelOne?
      Cybersecurity Built for What’s Next
    • Our Customers
      Trusted by the World’s Leading Enterprises
    • Industry Recognition
      Tested and Proven by the Experts
    • About Us
      The Industry Leader in Autonomous Cybersecurity
    Compare SentinelOne
    • Arctic Wolf
    • Broadcom
    • CrowdStrike
    • Cybereason
    • Microsoft
    • Palo Alto Networks
    • Sophos
    • Splunk
    • Trellix
    • Trend Micro
    • Wiz
    Verticals
    • Energy
    • Federal Government
    • Finance
    • Healthcare
    • Higher Education
    • K-12 Education
    • Manufacturing
    • Retail
    • State and Local Government
  • Services
    Managed Services
    • Managed Services Overview
      Wayfinder Threat Detection & Response
    • Threat Hunting
      World-Class Expertise and Threat Intelligence
    • Managed Detection & Response
      24/7/365 Expert MDR Across Your Entire Environment
    • Incident Readiness & Response
      DFIR, Breach Readiness, & Compromise Assessments
    Support, Deployment, & Health
    • Technical Account Management
      Customer Success with Personalized Service
    • SentinelOne GO
      Guided Onboarding & Deployment Advisory
    • SentinelOne University
      Live and On-Demand Training
    • Services Overview
      Comprehensive Solutions for Seamless Security Operations
    • SentinelOne Community
      Community Login
  • Partners
    Our Network
    • MSSP Partners
      Succeed Faster with SentinelOne
    • Singularity Marketplace
      Extend the Power of S1 Technology
    • Cyber Risk Partners
      Enlist Pro Response and Advisory Teams
    • Technology Alliances
      Integrated, Enterprise-Scale Solutions
    • SentinelOne for AWS
      Hosted in AWS Regions Around the World
    • Channel Partners
      Deliver the Right Solutions, Together
    • SentinelOne for Google Cloud
      Unified, Autonomous Security Giving Defenders the Advantage at Global Scale
    • Partner Locator
      Your Go-to Source for Our Top Partners in Your Region
    Partner Portal→
  • Resources
    Resource Center
    • Case Studies
    • Data Sheets
    • eBooks
    • Reports
    • Videos
    • Webinars
    • Whitepapers
    • Events
    View All Resources→
    Blog
    • Feature Spotlight
    • For CISO/CIO
    • From the Front Lines
    • Identity
    • Cloud
    • macOS
    • SentinelOne Blog
    Blog→
    Tech Resources
    • SentinelLABS
    • Ransomware Anthology
    • Cybersecurity 101
  • About
    About SentinelOne
    • About SentinelOne
      The Industry Leader in Cybersecurity
    • Investor Relations
      Financial Information & Events
    • SentinelLABS
      Threat Research for the Modern Threat Hunter
    • Careers
      The Latest Job Opportunities
    • Press & News
      Company Announcements
    • Cybersecurity Blog
      The Latest Cybersecurity Threats, News, & More
    • FAQ
      Get Answers to Our Most Frequently Asked Questions
    • DataSet
      The Live Data Platform
    • S Foundation
      Securing a Safer Future for All
    • S Ventures
      Investing in the Next Generation of Security, Data and AI
  • Pricing
Get StartedContact Us
CVE Vulnerability Database
Vulnerability Database/CVE-2025-59837

CVE-2025-59837: Astro Web Framework SSRF Vulnerability

CVE-2025-59837 is an SSRF vulnerability in Astro web framework's image proxy that allows attackers to bypass domain validation using backslashes. This post covers the technical details, affected versions, and mitigation steps.

Published: April 29, 2026

CVE-2025-59837 Overview

CVE-2025-59837 is a Server-Side Request Forgery (SSRF) vulnerability in Astro, a popular web framework for building content-driven websites. The vulnerability exists in Astro's image proxy functionality, where domain validation can be bypassed using backslashes in the href parameter. This bypass allows attackers to make server-side requests to arbitrary URLs, potentially leading to SSRF attacks and Cross-Site Scripting (XSS) exploitation.

This vulnerability represents an incomplete fix for CVE-2025-58179, indicating that the original mitigation was insufficient in preventing all forms of URL manipulation attacks.

Critical Impact

Attackers can bypass image proxy domain validation to access internal resources, exfiltrate sensitive data, or chain with XSS for client-side attacks against users.

Affected Products

  • Astro versions 5.13.4 through 5.13.9
  • Astro Node.js integrations using the image proxy feature
  • Applications utilizing Astro's remote image handling capabilities

Discovery Timeline

  • 2025-10-28 - CVE CVE-2025-59837 published to NVD
  • 2025-11-25 - Last updated in NVD database

Technical Details for CVE-2025-59837

Vulnerability Analysis

The vulnerability resides in Astro's isRemotePath function within the internal helpers package. This function is responsible for determining whether a given path should be treated as a remote URL, which is critical for the image proxy's domain validation logic.

The original implementation only checked for standard URL protocols and protocol-relative URLs (starting with //). However, it failed to account for backslash variants that can be normalized to valid remote URLs by browsers and URL parsers. For example, a path like \\example.com or %5C%5Cexample.com (URL-encoded backslashes) would not be detected as a remote path, allowing it to bypass the domain allowlist validation.

This bypass is particularly dangerous because when these malformed URLs are processed by downstream components or rendered in browsers, the backslashes may be normalized to forward slashes, resulting in valid remote URL requests.

Root Cause

The root cause stems from insufficient input validation in the URL path detection logic. The original isRemotePath function used a simple regex check (URL_PROTOCOL_REGEX) and a data: prefix check, but did not handle:

  1. Backslash-prefixed URLs (e.g., \\attacker.com)
  2. URL-encoded backslash variants (e.g., %5C%5Cexample.com)
  3. Protocol schemes with backslashes instead of forward slashes (e.g., http:\\attacker.com)

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can craft a malicious URL with backslash characters in the href parameter when requesting images through Astro's image proxy. The malformed URL bypasses domain validation, causing the server to make requests to attacker-controlled or internal resources.

typescript
  * - `ws://`
  * - `//` (protocol-relative URLs)
  * - `data:` (base64 images)
+ * - Backslash variants (e.g., `\\example.com`) that could normalize to remote URLs
+ * - URL-encoded backslash variants (e.g., `%5C%5Cexample.com`)
  * @param src
  */
 export function isRemotePath(src: string) {
-	return URL_PROTOCOL_REGEX.test(src) || src.startsWith('data:');
+	// First decode any URL-encoded backslashes
+	const decoded = src.replace(/%5C/gi, '\\');
+	
+	// Check for any backslash at the start (single or multiple)
+	// These can be normalized to protocol-relative URLs
+	if (decoded[0] === '\\') {
+		return true;
+	}
+	
+	// Check for protocols with backslashes (e.g., http:\\ or https:\\)
+	if (/^(?:http|https|ftp|ws):\\/.test(decoded)) {
+		return true;
+	}
+	
+	// Check standard URL patterns
+	return URL_PROTOCOL_REGEX.test(decoded) || decoded.startsWith('data:');
 }
 
 export function slash(path: string) {

Source: GitHub Commit Changes

Detection Methods for CVE-2025-59837

Indicators of Compromise

  • Unusual image proxy requests containing backslash characters (\ or %5C) in URL parameters
  • Server-side requests to unexpected internal IP ranges (e.g., 127.0.0.1, 10.x.x.x, 192.168.x.x, 169.254.169.254)
  • Outbound connections from the Astro application server to external domains not in the configured allowlist
  • Web application firewall (WAF) logs showing encoded backslash patterns in image-related endpoints

Detection Strategies

  • Deploy WAF rules to detect and block requests containing %5C or %5c URL-encoded backslashes in image proxy parameters
  • Implement network monitoring to alert on server-initiated requests to cloud metadata endpoints (e.g., 169.254.169.254)
  • Review application logs for anomalous patterns in image proxy request paths, particularly those with non-standard URL formats
  • Configure SentinelOne Singularity to monitor for SSRF-related network behaviors from web application processes

Monitoring Recommendations

  • Enable verbose logging for Astro's image proxy component to capture all incoming request URLs
  • Set up alerts for any outbound HTTP requests from the application server to internal network ranges
  • Monitor for XSS payload patterns in server responses that may indicate successful exploitation chaining
  • Implement request rate limiting on the image proxy endpoint to slow down potential automated exploitation attempts

How to Mitigate CVE-2025-59837

Immediate Actions Required

  • Upgrade Astro to version 5.13.10 or later immediately, which contains the complete fix for this vulnerability
  • If immediate upgrade is not possible, disable the image proxy feature temporarily until the patch can be applied
  • Review server logs for any signs of exploitation attempts using backslash-based URL bypass patterns
  • Audit any applications using Astro's image proxy to ensure they are not exposed to untrusted user input

Patch Information

The vulnerability has been fixed in Astro version 5.13.10. The fix enhances the isRemotePath function to properly detect and handle backslash variants, including URL-encoded backslashes. The patched version decodes potential URL-encoded characters before performing validation checks and explicitly checks for backslash-prefixed paths that could be normalized to remote URLs.

For detailed information about the security fix, see the GitHub Security Advisory. The fix was implemented across two commits: commit 1e2499e and commit 9ecf359.

Workarounds

  • Disable remote image handling in Astro configuration by removing domains from the image.remotePatterns configuration
  • Implement a reverse proxy or WAF rule to sanitize and reject requests containing backslash characters before they reach the Astro application
  • Restrict network egress from the application server to only necessary external domains using firewall rules
  • Use a content security policy (CSP) to limit the scope of potential XSS impact if the vulnerability is chained
bash
# Example: Upgrade Astro to the patched version
npm update astro@5.13.10

# Or using yarn
yarn upgrade astro@5.13.10

# Verify the installed version
npx astro --version

Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.

  • Vulnerability Details
  • TypeSSRF

  • Vendor/TechAstro

  • SeverityHIGH

  • CVSS Score7.2

  • EPSS Probability0.04%

  • Known ExploitedNo
  • CVSS Vector
  • CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
  • Impact Assessment
  • ConfidentialityLow
  • IntegrityNone
  • AvailabilityNone
  • CWE References
  • CWE-79
  • Technical References
  • GitHub Security Advisory
  • Vendor Resources
  • GitHub Commit Changes

  • GitHub Commit Changes
  • Related CVEs
  • CVE-2026-33769: Astro Web Framework SSRF Vulnerability

  • CVE-2026-27829: Astro Framework SSRF Vulnerability

  • CVE-2026-25545: Astro @astrojs/node SSRF Vulnerability

  • CVE-2026-41067: Astro Web Framework XSS Vulnerability
Default Legacy - Prefooter | Experience the World’s Most Advanced Cybersecurity Platform

Experience the World’s Most Advanced Cybersecurity Platform

See how our intelligent, autonomous cybersecurity platform can protect your organization now and into the future.

Try SentinelOne
  • Get Started
  • Get a Demo
  • Product Tour
  • Why SentinelOne
  • Pricing & Packaging
  • FAQ
  • Contact
  • Contact Us
  • Customer Support
  • SentinelOne Status
  • Language
  • Platform
  • Singularity Platform
  • Singularity Endpoint
  • Singularity Cloud
  • Singularity AI-SIEM
  • Singularity Identity
  • Singularity Marketplace
  • Purple AI
  • Services
  • Wayfinder TDR
  • SentinelOne GO
  • Technical Account Management
  • Support Services
  • Verticals
  • Energy
  • Federal Government
  • Finance
  • Healthcare
  • Higher Education
  • K-12 Education
  • Manufacturing
  • Retail
  • State and Local Government
  • Cybersecurity for SMB
  • Resources
  • Blog
  • Labs
  • Case Studies
  • Videos
  • Product Tours
  • Events
  • Cybersecurity 101
  • eBooks
  • Webinars
  • Whitepapers
  • Press
  • News
  • Ransomware Anthology
  • Company
  • About Us
  • Our Customers
  • Careers
  • Partners
  • Legal & Compliance
  • Security & Compliance
  • Investor Relations
  • S Foundation
  • S Ventures

©2026 SentinelOne, All Rights Reserved.

Privacy Notice Terms of Use

English