CVE-2021-43854

Published: 23 December 2021

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.

Priority

Cvss 3 Severity Score

7.5

Score breakdown

Status

Package	Release	Status
nltk Launchpad, Ubuntu, Debian	bionic	Needs triage
	focal	Needs triage
	hirsute	Ignored (end of life)
	impish	Ignored (end of life)
	jammy	Needs triage
	kinetic	Ignored (end of life, was needs-triage)
	lunar	Not vulnerable (3.7-1)
	mantic	Not vulnerable (3.7-1)
	noble	Not vulnerable (3.7-1)
	trusty	Needs triage
	upstream	Released (3.6.6)
	xenial	Needs triage
	Patches: upstream: https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341

Severity score breakdown

Parameter	Value
Base score	7.5
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	None
Availability impact	High
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

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