CVE-2017-16117 in slug
Summary
by MITRE
slug is a module to slugify strings, even if they contain unicode. slug is vulnerable to regular expression denial of service is specially crafted untrusted input is passed as input. About 50k characters can block the event loop for 2 seconds.
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Analysis
by VulDB Data Team • 03/21/2023
The CVE-2017-16117 vulnerability affects the slug module, a popular npm package used for converting strings into URL-friendly slugs while handling unicode characters. This module processes input strings to remove special characters and normalize text for web applications. The vulnerability stems from the module's insufficient protection against regular expression denial of service attacks, where specially crafted malicious input can cause significant performance degradation. When untrusted input containing specific patterns is passed to the slugify function, the regular expressions used internally can be exploited to create computationally expensive operations.
The technical flaw manifests through the module's regex patterns that are susceptible to catastrophic backtracking when processing malformed input. The vulnerability allows an attacker to craft input strings that cause the regular expression engine to perform an exponential number of operations, effectively blocking the JavaScript event loop. This behavior can result in the event loop being blocked for approximately two seconds when processing input containing around 50,000 characters, making the application unresponsive during this period. The vulnerability is classified as a regular expression denial of service attack pattern that aligns with CWE-400 and specifically relates to CWE-1321 which addresses regex denial of service in JavaScript environments.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially enable more serious attacks such as service disruption and resource exhaustion. Applications using the vulnerable slug module become susceptible to denial of service conditions where legitimate users may experience application slowdowns or complete unresponsiveness. This vulnerability is particularly concerning in web applications where user input is processed through the slugify function, as attackers can exploit it to create sustained denial of service conditions. The attack vector aligns with ATT&CK technique T1499.004 which covers network denial of service attacks and represents a common pattern of resource exhaustion attacks in web applications.
Mitigation strategies for CVE-2017-16117 include immediate upgrading to a patched version of the slug module where available, implementing input validation and sanitization before processing strings through the slugify function, and applying rate limiting to prevent abuse of the vulnerable functionality. Organizations should also consider implementing regex validation to detect and reject potentially malicious input patterns that could trigger the vulnerable regular expressions. The fix typically involves rewriting the regular expressions to prevent catastrophic backtracking or implementing proper input length limits to prevent excessive processing time. Additionally, monitoring systems should be configured to detect unusual processing times or resource consumption patterns that may indicate exploitation attempts. Security teams should also consider implementing defensive programming practices such as timeout mechanisms for string processing operations and input length restrictions to prevent exploitation of similar vulnerabilities in other modules.