CVE-2021-43854

Advisory

Nltk 3.6.5 includes a fix for CVE-2021-43854: Versions prior to 3.6.5 are vulnerable to regular expression denial of service (ReDoS) attacks. The vulnerability is present in PunktSentenceTokenizer, sent_tokenize and word_tokenize. Any users of this class, or these two functions, are vulnerable to the ReDoS attack. In short, a specifically crafted long input to any of these vulnerable functions will cause them to take a significant amount of execution time. If your program relies on any of the vulnerable functions for tokenizing unpredictable user input, it's strongly recommended upgrading to a version of NLTK without the vulnerability. For users unable to upgrade the execution time can be bounded by limiting the maximum length of an input to any of the vulnerable functions.
https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
https://github.com/nltk/nltk/issues/2866

Affected package

Affected versions

Fixed versions

Vulnerability changelog

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Versions prior to 3.6.5 are vulnerable to regular expression denial of service (ReDoS) attacks. The vulnerability is present in PunktSentenceTokenizer, sent_tokenize and word_tokenize. Any users of this class, or these two functions, are vulnerable to the ReDoS attack. In short, a specifically crafted long input to any of these vulnerable functions will cause them to take a significant amount of execution time. If your program relies on any of the vulnerable functions for tokenizing unpredictable user input, then we would strongly recommend upgrading to a version of NLTK without the vulnerability. For users unable to upgrade the execution time can be bounded by limiting the maximum length of an input to any of the vulnerable functions. Our recommendation is to implement such a limit. See CVE-2021-43854.


CONFIRM:https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x: https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
MISC:https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341: https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
MISC:https://github.com/nltk/nltk/issues/2866: https://github.com/nltk/nltk/issues/2866
MISC:https://github.com/nltk/nltk/pull/2869: https://github.com/nltk/nltk/pull/2869

Resources

• https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
• https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
• https://github.com/nltk/nltk/issues/2866
• https://github.com/nltk/nltk/pull/2869
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43854