CVE-2024-10491: OpenJSF Express Injection Vulnerability

CVE-2024-10491 Overview

A vulnerability has been identified in the Express.js response.links function, allowing for arbitrary resource injection in the Link header when unsanitized data is used. The issue arises from improper sanitization in Link header values, which can allow a combination of characters like ,, ;, and <> to preload malicious resources. This vulnerability is especially relevant for dynamic parameters in web applications built on the Express.js framework.

Critical Impact

Attackers can inject arbitrary resources into Link headers, potentially enabling resource preloading attacks, cache poisoning, or manipulation of browser behavior through maliciously crafted header values.

Affected Products

• OpenJS Foundation Express for Node.js
• Applications using the response.links function with unsanitized user input
• Express-based web applications processing dynamic Link header parameters

Discovery Timeline

• 2024-10-29 - CVE CVE-2024-10491 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2024-10491

Vulnerability Analysis

This vulnerability is classified as an Injection vulnerability (CWE-74) affecting the Express.js framework's response.links function. The core issue stems from insufficient input validation when constructing Link headers from user-supplied data. When application developers pass unsanitized input to the response.links function, attackers can craft malicious payloads containing special characters that break out of the intended header structure.

The Link header is commonly used for resource hints, preloading assets, and pagination in RESTful APIs. By exploiting this vulnerability, an attacker could inject additional Link header directives, potentially causing the browser to preload malicious resources or manipulate caching behavior.

Root Cause

The root cause lies in improper sanitization of values passed to the response.links function in Express.js. The function does not adequately escape or validate characters with special meaning in Link header syntax, specifically:

• Comma (,) - used to separate multiple link values
• Semicolon (;) - used to separate link parameters
• Angle brackets (<>) - used to delimit URIs

When user input containing these characters is passed directly to response.links, it can alter the structure of the resulting Link header in unintended ways.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by providing specially crafted input to any application endpoint that passes user-controlled data to the response.links function. The malicious input would contain Link header metacharacters that, when processed without sanitization, inject additional resources or modify existing link directives.

For example, if an application constructs pagination links using user input, an attacker could inject additional preload directives pointing to malicious resources. This could potentially be leveraged for phishing, malware distribution, or cache poisoning attacks depending on how downstream systems process the manipulated headers.

Detection Methods for CVE-2024-10491

Indicators of Compromise

• Unusual characters (,, ;, <>) in URL parameters or user input fields that are used to construct Link headers
• Malformed or unexpected Link headers in HTTP responses
• Server logs showing injection attempts with Link header metacharacters
• Unexpected resource preloading or fetch requests originating from application responses

Detection Strategies

• Implement input validation monitoring to detect special characters in parameters passed to response header functions
• Deploy web application firewall (WAF) rules to detect Link header injection patterns
• Monitor application logs for requests containing Link header metacharacters in unexpected fields
• Use runtime application self-protection (RASP) tools to detect header manipulation attempts

Monitoring Recommendations

• Enable detailed logging for all Express.js middleware and response handling
• Monitor for anomalous Link header structures in outbound HTTP responses
• Set up alerts for high-frequency requests with special characters in query parameters
• Review application code for instances where user input is passed to response.links without sanitization

How to Mitigate CVE-2024-10491

Immediate Actions Required

• Audit all application code for usage of the response.links function with user-controlled input
• Implement strict input validation and sanitization before passing data to response.links
• Consider using allowlist-based validation for any dynamic Link header values
• Update Express.js to the latest patched version when available

Patch Information

Organizations should monitor the HeroDevs vulnerability advisory for patch information and updates. Until an official patch is available, implementing input validation and sanitization is the recommended mitigation strategy.

Workarounds

• Sanitize all user input before passing to response.links by removing or encoding ,, ;, and <> characters
• Implement a custom wrapper function for response.links that validates input against an allowlist of acceptable characters
• Avoid using dynamic user input in Link header construction where possible
• Use Content Security Policy (CSP) headers to restrict resource loading and mitigate potential exploitation impact

# Example: Input validation for Express.js response.links
# Implement sanitization middleware to strip Link header metacharacters
# Filter out: comma (,), semicolon (;), angle brackets (<>)
# 
# Apply to all routes that use response.links with dynamic parameters
# Consider using a library like validator.js for consistent sanitization