CVE-2016-10539 in negotiator
Summary
by MITRE
negotiator is an HTTP content negotiator for Node.js and is used by many modules and frameworks including Express and Koa. The header for "Accept-Language", when parsed by negotiator 0.6.0 and earlier is vulnerable to Regular Expression Denial of Service via a specially crafted string.
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Analysis
by VulDB Data Team • 02/10/2020
The vulnerability identified as CVE-2016-10539 affects negotiator, a popular HTTP content negotiator module for Node.js that serves as a foundational component for numerous web frameworks including Express and Koa. This module handles HTTP content negotiation processes, specifically parsing the Accept-Language header to determine appropriate content localization. The flaw manifests in the regular expression pattern used to parse the Accept-Language header, creating a critical security weakness that can be exploited through carefully crafted malicious input strings.
The technical implementation of this vulnerability stems from the use of inefficient regular expressions within the negotiator module version 0.6.0 and earlier. When processing a specially crafted Accept-Language header, the regular expression engine enters into a catastrophic backtracking scenario where the parsing algorithm exponentially increases processing time as input complexity grows. This behavior creates a denial of service condition where legitimate requests can be delayed or blocked entirely, effectively rendering the affected service unavailable to genuine users. The vulnerability maps directly to CWE-400, which categorizes regular expression denial of service attacks as a specific weakness in software design and implementation.
The operational impact of CVE-2016-10539 extends beyond simple service disruption, as it affects a core dependency that many Node.js applications rely upon for proper content negotiation. When exploited, the vulnerability allows attackers to consume excessive computational resources through malformed Accept-Language headers, potentially leading to system resource exhaustion and application unavailability. The attack surface is particularly broad since negotiator is used across multiple web frameworks, meaning that a single vulnerable component can compromise entire application stacks. This vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how dependencies can become attack vectors in modern software ecosystems.
Mitigation strategies for CVE-2016-10539 require immediate action to update the negotiator module to version 0.6.1 or later, where the regular expression parsing has been corrected to prevent catastrophic backtracking. Organizations should implement comprehensive dependency monitoring to identify and remediate similar vulnerabilities across their software supply chains. Additionally, input validation and rate limiting mechanisms should be deployed at network boundaries to detect and prevent exploitation attempts. The fix implemented in newer versions addresses the core parsing logic by using more efficient regular expressions and implementing proper input length restrictions, aligning with security best practices outlined in OWASP Top Ten and NIST guidelines for secure coding practices.