CVE-2016-10535

Vulnerability

csrf-lite is a cross-site request forgery (CSRF) protection library for framework-less Node.js sites. Versions before 0.1.2 use the === operator for comparing CSRF tokens, which is a fail-first string comparison instead of a constant-time comparison. This design flaw allows an attacker to exploit timing differences to guess the secret token. [1][2]

Exploitation

An attacker needs network proximity to measure subtle timing differences in the server's response. By sending requests with guessed token values and observing the response times, they can deduce each character of the secret sequentially. Under favorable network conditions, the secret can be guessed in no more than (16*18) = 288 guesses, compared to the 16^18 guesses required if a constant-time comparison were used. [1][2]

Impact

Successful exploitation enables the attacker to forge valid CSRF tokens, thereby bypassing the CSRF protection. This allows the attacker to perform actions on behalf of an authenticated user, leading to potential unauthorized state changes, such as modifying account settings or submitting forms. [1][2]

Mitigation

The vulnerability was fixed in version 0.1.2 of csrf-lite, which replaced the === comparison with a constant-time string comparison using the scmp library. [3] Users should update to version 0.1.2 or later. No workarounds are available for earlier versions. [2]