CVE-2021-43854 : Exploit Details and Defense Strategies
Learn about CVE-2021-43854, a vulnerability in NLTK versions below 3.6.5 that enables ReDoS attacks. Discover impact, affected systems, exploitation details, and mitigation steps.
NLTK (Natural Language Toolkit) versions prior to 3.6.5 are vulnerable to regular expression denial of service (ReDoS) attacks, affecting the PunktSentenceTokenizer, sent_tokenize, and word_tokenize functions.
Understanding CVE-2021-43854
What is CVE-2021-43854?
NLTK, a suite of Python modules for Natural Language Processing, is susceptible to ReDoS attacks due to inefficient regular expression complexity in versions below 3.6.5.
The Impact of CVE-2021-43854
The vulnerability allows attackers to cause significant delays by providing specially crafted long inputs to the affected NLTK functions, leading to a high impact on system availability.
Technical Details of CVE-2021-43854
Vulnerability Description
- The vulnerability stems from unbounded resource consumption by specific NLTK functions, making them slow and susceptible to ReDoS attacks.
Affected Systems and Versions
- Product: NLTK
- Vendor: NLTK
- Versions Affected: < 3.6.5
Exploitation Mechanism
- Attack Complexity: Low
- Attack Vector: Network
- Impact: High
- Privileges Required: None
Mitigation and Prevention
Immediate Steps to Take
- Upgrade NLTK to a version above 3.6.5 to eliminate the vulnerability.
- Implement input length restrictions on the vulnerable functions to limit execution time.
Long-Term Security Practices
- Regularly update NLTK and other dependencies to stay protected against known vulnerabilities.
- Conduct security audits to detect and mitigate potential risks in code.
Patching and Updates
- Apply patches released by NLTK promptly to address security issues and improve system resilience.