CVE-2021-43854
NLTK Regular Expression Denial of Service (ReDoS) Vulnerability
Description
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.
INFO
Published Date :
Dec. 23, 2021, 6:15 p.m.
Last Modified :
Jan. 4, 2022, 4:38 p.m.
Source :
[email protected]
Remotely Exploitable :
Yes !
Impact Score :
3.6
Exploitability Score :
3.9
Public PoC/Exploit Available at Github
CVE-2021-43854 has a 2 public PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2021-43854.
| URL | Resource |
|---|---|
| https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341 | Patch Third Party Advisory |
| https://github.com/nltk/nltk/issues/2866 | Exploit Issue Tracking Patch Third Party Advisory |
| https://github.com/nltk/nltk/pull/2869 | Exploit Patch Third Party Advisory |
| https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x | Exploit Patch Third Party Advisory |
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Research CVEs
List of RegEx DoS (ReDoS) CVEs and resources
security awesome redos regex dos regex-dos pentesting awesome-list regex-security
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2021-43854 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2021-43854 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Modified by [email protected]
May. 14, 2024
Action Type Old Value New Value -
Initial Analysis by [email protected]
Jan. 04, 2022
Action Type Old Value New Value Added CVSS V2 NIST (AV:N/AC:L/Au:N/C:N/I:N/A:P) Changed Reference Type https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341 No Types Assigned https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341 Patch, Third Party Advisory Changed Reference Type https://github.com/nltk/nltk/issues/2866 No Types Assigned https://github.com/nltk/nltk/issues/2866 Exploit, Issue Tracking, Patch, Third Party Advisory Changed Reference Type https://github.com/nltk/nltk/pull/2869 No Types Assigned https://github.com/nltk/nltk/pull/2869 Exploit, Patch, Third Party Advisory Changed Reference Type https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x No Types Assigned https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x Exploit, Patch, Third Party Advisory Added CPE Configuration OR *cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:* versions up to (excluding) 3.6.5
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2021-43854 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2021-43854
weaknesses.
Exploit Prediction
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days.
0.37 }} 0.06%
score
0.73070
percentile