Denial of service in NLTK

1) Inefficient regular expression complexity

EUVDB-ID: #VU105953

Risk: Medium

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-3828

CWE-ID: CWE-1333 - Inefficient Regular Expression Complexity

Exploit availability: No

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to insufficient input validation when processing untrusted input with a regular expressions. A remote attacker can pass specially crafted data to the application and perform regular expression denial of service (ReDos) attack.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Natural Language Toolkit: 2.0.1 - 3.6.3

CPE2.3

• cpe:2.3:a:nltk.org:nltk:2.0.1:*:*:*:*:*:*:*
• cpe:2.3:a:nltk.org:nltk:2.0.3:*:*:*:*:*:*:*
• cpe:2.3:a:nltk.org:nltk:2.0.4:*:*:*:*:*:*:*

External links

https://huntr.dev/bounties/d19aed43-75bc-4a03-91a0-4d0bb516bc32
https://github.com/nltk/nltk/commit/277711ab1dec729e626b27aab6fa35ea5efbd7e6

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.