CVE-2021-3820 in inflect
Summary
by MITRE • 09/27/2021
inflect is vulnerable to Inefficient Regular Expression Complexity
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Analysis
by VulDB Data Team • 10/02/2021
The vulnerability identified as CVE-2021-3820 affects the inflect library, which is commonly used for text processing and natural language manipulation in various applications. This library implements regular expressions to perform pattern matching and text transformations, making it a critical component in many software systems. The vulnerability stems from inefficient regular expression complexity that can be exploited to cause denial of service attacks through resource exhaustion. When malicious input is processed through the inflect library, the regular expressions can trigger exponential time complexity behavior, leading to significant performance degradation or complete system unresponsiveness.
The technical flaw manifests in the way the inflect library handles certain regular expression patterns during text processing operations. Specifically, the library employs regular expressions that are susceptible to catastrophic backtracking when processing malformed or specially crafted input strings. This occurs when the regular expression engine must explore an exponential number of possible matching paths due to overlapping or ambiguous patterns in the expression. The vulnerability is classified under CWE-1333 which specifically addresses inefficient regular expression complexity and falls within the broader category of denial of service attacks. The attack vector typically involves sending carefully constructed input data that causes the regular expression engine to consume excessive computational resources, potentially leading to system crashes or resource exhaustion.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially compromise entire system availability. Applications that rely on inflect for text processing, data validation, or natural language operations become vulnerable to denial of service attacks when processing untrusted input. Attackers can exploit this vulnerability by submitting malicious input that triggers the inefficient regular expression patterns, causing the system to consume excessive CPU cycles and memory resources. This makes the vulnerability particularly dangerous in web applications, APIs, and any system that processes user-provided data through the inflect library. The impact is especially severe in environments where the library is used extensively or in high-throughput scenarios where resource exhaustion can lead to cascading failures across dependent services.
Mitigation strategies for CVE-2021-3820 involve both immediate remediation and long-term architectural improvements. The primary solution is to update to a patched version of the inflect library that addresses the inefficient regular expression complexity issues. Security teams should also implement input validation and sanitization measures to prevent malicious patterns from reaching the vulnerable library functions. Additionally, rate limiting and resource monitoring should be implemented to detect and prevent exploitation attempts before they can cause significant damage. Organizations should consider implementing regular security assessments and penetration testing to identify similar vulnerabilities in other third-party libraries and dependencies. The ATT&CK framework categorizes this vulnerability under T1499 which covers resource exhaustion attacks, and defensive measures should align with the mitigation strategies outlined in the framework for preventing and detecting such attacks. System administrators should also establish monitoring protocols that can detect unusual resource consumption patterns that may indicate exploitation attempts.