CVE-2025-2691: Nossrf Package SSRF Vulnerability

CVE-2025-2691 Overview

CVE-2025-2691 is a Server-Side Request Forgery (SSRF) vulnerability affecting the nossrf npm package, a library specifically designed to protect applications against SSRF attacks. Versions prior to 1.0.4 contain a flaw that allows attackers to bypass the SSRF protection mechanism by providing hostnames that resolve to local or reserved IP address spaces.

Critical Impact

This vulnerability undermines the core security function of the nossrf library, potentially allowing attackers to access internal services, cloud metadata endpoints, and other protected resources that should be inaccessible from external requests.

Affected Products

• nossrf versions prior to 1.0.4
• Applications using vulnerable nossrf versions for SSRF protection
• Node.js applications relying on nossrf for URL validation

Discovery Timeline

• 2025-03-23 - CVE-2025-2691 published to NVD
• 2025-03-26 - Last updated in NVD database

Technical Details for CVE-2025-2691

Vulnerability Analysis

This SSRF vulnerability exists in the nossrf package's hostname resolution and validation logic. The nossrf library is designed to prevent SSRF attacks by blocking requests to internal IP addresses and reserved address spaces. However, the vulnerable versions fail to properly handle certain hostname configurations that ultimately resolve to restricted IP ranges.

The vulnerability allows attackers to craft malicious hostnames that pass the initial validation checks but resolve to local addresses (such as 127.0.0.1, localhost, or 0.0.0.0) or private IP ranges (like 10.x.x.x, 172.16.x.x-172.31.x.x, or 192.168.x.x). This bypass technique exploits timing differences between DNS resolution phases or DNS rebinding attacks where the hostname resolves to a safe IP during validation but to a malicious internal IP during the actual request.

The network-based attack vector means exploitation can occur remotely without authentication, making this vulnerability particularly concerning for internet-facing applications that rely on nossrf for SSRF protection.

Root Cause

The root cause stems from inadequate validation of DNS resolution results in the nossrf library. The package fails to properly verify that resolved IP addresses remain outside of restricted address spaces at all stages of the request lifecycle. This creates a race condition where DNS responses can be manipulated between the validation check and the actual HTTP request execution.

Attack Vector

Attackers can exploit this vulnerability by submitting URLs with specially crafted hostnames to applications protected by vulnerable nossrf versions. The attack leverages DNS resolution behaviors to bypass IP-based blocklists.

Common attack techniques include:

• DNS rebinding attacks where the attacker controls a DNS server that returns different IP addresses for the same hostname
• Using hostnames that resolve to IPv6 representations of localhost or private addresses
• Exploiting URL parsing inconsistencies between the validation layer and the HTTP client

Successful exploitation enables attackers to reach internal services, access cloud provider metadata endpoints (such as 169.254.169.254), scan internal networks, or exfiltrate sensitive data from protected resources.

Detection Methods for CVE-2025-2691

Indicators of Compromise

• Unexpected outbound requests to internal IP addresses from application servers
• DNS queries for suspicious or attacker-controlled domains from protected applications
• Access logs showing requests to cloud metadata endpoints (e.g., 169.254.169.254)
• Unusual network traffic patterns targeting private IP ranges from web-facing services

Detection Strategies

• Audit package.json and package-lock.json files for nossrf versions below 1.0.4
• Implement network monitoring to detect anomalous internal service access patterns
• Use software composition analysis (SCA) tools to identify vulnerable dependencies
• Monitor DNS resolution logs for suspicious rebinding patterns or rapid IP changes

Monitoring Recommendations

• Enable detailed logging for all URL validation and HTTP request operations
• Configure network egress monitoring to alert on requests to internal IP ranges
• Implement cloud provider metadata endpoint blocking at the infrastructure level
• Set up automated dependency scanning in CI/CD pipelines to detect vulnerable packages

How to Mitigate CVE-2025-2691

Immediate Actions Required

• Upgrade nossrf to version 1.0.4 or later immediately
• Audit applications to identify all instances of nossrf usage
• Review application logs for signs of SSRF exploitation attempts
• Implement additional network-level controls to restrict outbound requests to internal resources

Patch Information

The vulnerability has been addressed in nossrf version 1.0.4. Organizations should update their dependencies by running npm update nossrf or explicitly specifying version 1.0.4 or higher in their package.json file. The Snyk Vulnerability Report provides additional details on the remediation.

Workarounds

• Implement network-level egress filtering to block requests to internal IP ranges and cloud metadata endpoints
• Add a secondary validation layer that verifies resolved IP addresses before making requests
• Use firewall rules to restrict application server outbound access to only necessary external endpoints
• Consider implementing a proxy server that enforces strict URL validation and IP blocking

# Update nossrf to the patched version
npm update nossrf

# Or explicitly install the fixed version
npm install nossrf@1.0.4

# Verify the installed version
npm list nossrf