CVE-2016-10535 in csrf-lite
Summary
by MITRE
csrf-lite is a cross-site request forgery protection library for framework-less node sites. csrf-lite uses `===`, a fail first string comparison, instead of a time constant string comparison This enables an attacker to guess the secret in no more than (16*18)288 guesses, instead of the 16^18 guesses required were the timing attack not present.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2016-10535 affects the csrf-lite library, a cross-site request forgery protection mechanism designed for node.js applications that do not utilize a full web framework. This library implements security controls to prevent unauthorized actions from being executed on behalf of authenticated users, making it a critical component in web application security. The flaw resides in the implementation of string comparison operations within the library's core functionality, specifically how it validates CSRF tokens against expected values. When an attacker can exploit timing variations in string comparison operations, they gain a significant advantage in bypassing security measures that rely on secret token validation. The vulnerability stems from the use of the strict equality operator === in JavaScript, which performs an immediate comparison without any timing considerations that would otherwise obscure the comparison process.
The technical implementation flaw represents a classic timing attack vulnerability that falls under CWE-376, which describes the improper handling of timing information in security-sensitive operations. The csrf-lite library uses a fail-first string comparison approach where the comparison stops as soon as a mismatch is detected, creating observable timing differences that attackers can exploit. This approach is fundamentally flawed because it provides attackers with timing information that reveals whether characters in the secret match the expected values. In a properly implemented constant-time comparison, the execution time should remain consistent regardless of the input values, making timing-based attacks ineffective. However, the current implementation allows an attacker to perform a brute-force attack where they can determine the secret through significantly reduced attempts - specifically from 16^18 possible combinations down to just 288 guesses, representing an astronomical reduction in required computational effort.
The operational impact of this vulnerability is severe as it fundamentally undermines the security guarantees provided by the CSRF protection mechanism. An attacker who can perform timing-based attacks against the csrf-lite library can effectively bypass CSRF protection entirely, potentially allowing them to execute unauthorized actions on behalf of authenticated users. This vulnerability is particularly dangerous in environments where CSRF tokens are used to protect sensitive operations such as account modifications, financial transactions, or administrative functions. The reduced guesswork from 16^18 to 288 attempts means that even relatively weak secrets can be compromised within minutes or hours using automated tools. The attack vector is particularly concerning because it requires no special privileges or complex exploitation techniques, making it accessible to attackers with basic knowledge of timing attacks and web application security. This vulnerability directly impacts the CIA triad by weakening the integrity and availability of the protected web applications, as unauthorized modifications can occur without detection.
Mitigation strategies for this vulnerability require immediate attention and implementation of proper constant-time string comparison algorithms throughout the csrf-lite library and any applications using it. The recommended approach involves replacing the current string comparison implementation with a function that ensures constant execution time regardless of input values, typically using bitwise operations or similar techniques that prevent timing variations. Organizations should also consider implementing additional security layers such as rate limiting, enhanced secret generation algorithms, and monitoring for unusual patterns in authentication attempts. The remediation process must include thorough code review to identify all instances where similar timing vulnerabilities might exist within the application's security mechanisms. Security teams should also implement proper dependency management practices to ensure that vulnerable libraries are promptly updated or replaced with secure alternatives. From an ATT&CK framework perspective, this vulnerability relates to T1190 - Exploit Public-Facing Application and T1078 - Valid Accounts, as it allows attackers to bypass application security controls and potentially escalate privileges through unauthorized actions. The vulnerability demonstrates the critical importance of implementing security measures that do not leak timing information, as this type of information can be exploited to significantly reduce the complexity of attacks against security mechanisms.