CVE-2026-31017: ERPNext & Frappe SSRF Vulnerability

CVE-2026-31017 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in the Print Format functionality of ERPNext v16.0.1 and Frappe Framework v16.1.1. The vulnerability arises from insufficient sanitization of user-supplied HTML content before it is rendered into PDF format. When generating PDFs from user-controlled HTML content, the application permits the inclusion of HTML elements such as <iframe> tags that reference external resources. The PDF rendering engine automatically fetches these resources on the server side, enabling attackers to force the server to make arbitrary HTTP requests to internal services, including cloud metadata endpoints.

Critical Impact

Attackers can exploit this SSRF vulnerability to access internal services and cloud metadata endpoints, potentially leading to sensitive information disclosure including cloud credentials and internal network reconnaissance.

Affected Products

• ERPNext v16.0.1
• Frappe Framework v16.1.1
• Systems using vulnerable PDF rendering with user-controlled HTML content

Discovery Timeline

• 2026-04-08 - CVE-2026-31017 published to NVD
• 2026-04-09 - Last updated in NVD database

Technical Details for CVE-2026-31017

Vulnerability Analysis

This SSRF vulnerability (CWE-918) exists within the PDF generation workflow of the Print Format functionality. The core issue stems from the application's failure to properly validate and sanitize HTML content before passing it to the PDF rendering engine. When a user supplies HTML content containing elements that reference external URLs (such as <iframe>, <img>, <link>, or similar tags), the server-side PDF renderer automatically resolves and fetches these resources.

The vulnerability is particularly dangerous in cloud environments where metadata services are accessible via well-known internal IP addresses (such as 169.254.169.254 for AWS, Azure, and GCP metadata endpoints). An attacker with the ability to submit custom HTML content for PDF generation can craft payloads that force the server to make requests to these internal endpoints, exfiltrating sensitive information including temporary credentials, instance metadata, and network configuration details.

Root Cause

The root cause of this vulnerability is insufficient input validation and sanitization within the Print Format functionality. The application accepts user-supplied HTML content and passes it directly to the PDF rendering engine without implementing an allowlist for permitted HTML elements or URL schemes. The PDF renderer then processes all embedded resources, including those pointing to internal network addresses, without any server-side validation of the target URLs.

This represents a failure to implement defense-in-depth principles, where user input destined for server-side processing should be strictly validated against known-safe patterns, and outbound requests from the server should be restricted to legitimate external resources only.

Attack Vector

The attack leverages the network-accessible PDF generation functionality. An attacker can craft malicious HTML content containing embedded resources pointing to internal services or cloud metadata endpoints. When this content is submitted for PDF rendering, the server automatically fetches the referenced resources, effectively acting as a proxy for the attacker's requests.

A typical attack scenario involves embedding HTML elements that reference the cloud provider's metadata service. The PDF rendering engine processes these elements, makes HTTP requests to the internal endpoints, and potentially includes the response data in the generated PDF or leaks it through other channels.

For technical details and proof-of-concept information, security researchers can reference the GitHub PoC repository for CVE-2026-31017.

Detection Methods for CVE-2026-31017

Indicators of Compromise

• Unusual outbound HTTP requests from the application server to internal IP ranges (e.g., 169.254.169.254, 127.0.0.1, 10.x.x.x, 192.168.x.x)
• PDF generation requests containing suspicious HTML elements with src, href, or data attributes pointing to internal resources
• Anomalous access patterns to cloud metadata endpoints from application servers
• Server logs showing requests to non-standard ports or internal service endpoints during PDF generation operations

Detection Strategies

• Implement network-level monitoring for outbound connections from PDF rendering services to internal IP ranges and cloud metadata endpoints
• Deploy web application firewall (WAF) rules to detect and block HTML content containing references to internal IP addresses or localhost
• Configure intrusion detection systems (IDS) to alert on SSRF-related patterns in HTTP request payloads
• Monitor application logs for PDF generation requests with embedded iframe, object, or embed elements containing suspicious URLs

Monitoring Recommendations

• Enable verbose logging for the PDF generation functionality to capture all processed HTML content
• Set up alerts for any outbound requests from the application tier to cloud metadata endpoints (169.254.169.254)
• Implement network segmentation monitoring to detect lateral movement attempts following potential credential exfiltration
• Deploy SentinelOne Singularity Platform to gain visibility into server-side request patterns and detect anomalous network behavior indicative of SSRF exploitation

How to Mitigate CVE-2026-31017

Immediate Actions Required

• Review and audit all PDF generation functionality for user-controlled HTML input
• Implement strict allowlisting of permitted HTML elements and attributes in Print Format content
• Block outbound requests from PDF rendering services to internal IP ranges and cloud metadata endpoints at the network level
• Consider disabling the Print Format functionality temporarily if it accepts arbitrary user HTML input until patches are applied
• Apply network segmentation to isolate PDF rendering services from sensitive internal resources

Patch Information

Organizations should monitor the Frappe security page and official ERPNext release channels for security updates addressing this vulnerability. Upgrade ERPNext and Frappe Framework to patched versions as soon as they become available. Review the GitHub advisory for CVE-2026-31017 for additional technical details.

Workarounds

• Implement server-side URL validation that blocks requests to private IP ranges (RFC 1918 addresses), localhost, and cloud metadata endpoints
• Deploy a proxy or firewall rule that prevents the application server from making outbound requests to 169.254.169.254 and other metadata service IPs
• Sanitize HTML input using a strict allowlist approach, removing or neutralizing elements that can trigger server-side resource fetching
• Consider rendering PDFs in a sandboxed environment with restricted network access

# Example: Block cloud metadata access using iptables
# Apply on servers running PDF rendering services
iptables -A OUTPUT -d 169.254.169.254 -j DROP
iptables -A OUTPUT -d 127.0.0.0/8 -p tcp --dport 80 -j DROP
iptables -A OUTPUT -d 127.0.0.0/8 -p tcp --dport 443 -j DROP
iptables -A OUTPUT -d 10.0.0.0/8 -j LOG --log-prefix "SSRF-ATTEMPT: "