CVE-2017-16116 in string
Summary
by MITRE
The string module is a module that provides extra string operations. The string module is vulnerable to regular expression denial of service when specifically crafted untrusted user input is passed into the underscore or unescapeHTML methods.
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Analysis
by VulDB Data Team • 03/21/2023
The vulnerability identified as CVE-2017-16116 resides within the string module, a component designed to extend standard string manipulation capabilities in various programming environments. This module provides additional utilities for processing text data and is commonly integrated into applications requiring enhanced string handling functionality. The flaw manifests specifically when the module processes untrusted input through two designated methods: underscore and unescapeHTML. These methods are intended to perform specific string transformations but become susceptible to malicious input patterns that trigger excessive computational overhead.
The technical implementation of this vulnerability stems from inadequate input validation and insufficient protection against malicious regular expression patterns. When crafted user input is passed through the underscore or unescapeHTML methods, the regular expressions used internally can be manipulated to cause exponential backtracking behavior. This occurs because the regular expressions lack proper bounds checking and fail to account for pathological input patterns that can cause the regex engine to explore an enormous number of possible matching combinations. The vulnerability maps to CWE-400, which specifically addresses uncontrolled resource consumption, and represents a classic example of regular expression denial of service attacks where computational resources are exhausted through carefully constructed input sequences.
The operational impact of CVE-2017-16116 extends beyond simple service disruption to potentially enable more sophisticated attack vectors within applications that utilize the vulnerable string module. An attacker could exploit this vulnerability to consume excessive CPU cycles and memory resources, leading to system performance degradation or complete service unavailability. The attack surface is particularly concerning in web applications where user input flows directly into these methods without proper sanitization, as demonstrated through ATT&CK technique T1499.001 for network denial of service. Applications using the string module in environments with limited computational resources or those handling high volumes of user requests face heightened risk of exploitation, as the vulnerability can be leveraged to create sustained denial of service conditions.
Mitigation strategies for this vulnerability should focus on implementing robust input validation and sanitization mechanisms before any data enters the vulnerable methods. Organizations should consider upgrading to patched versions of the string module where available, as the maintainers have addressed the regex patterns to prevent catastrophic backtracking scenarios. Additionally, implementing regular expression timeouts and resource limits within the application environment can provide defense-in-depth protection. Security teams should also consider implementing monitoring and alerting mechanisms to detect unusual resource consumption patterns that may indicate exploitation attempts. The remediation approach aligns with defensive programming practices outlined in CWE-134 and should be integrated into broader application security testing protocols including static analysis and dynamic testing to identify similar vulnerabilities in other regex implementations within the codebase.