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Ubuntu Security Notice USN-7365-1
March 24, 2025

nltk vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS

Summary:

Several security issues were fixed in NLTK.

Software Description:
- nltk: Natural Language Toolkit

Details:

It was discovered that NLTK contained a regex that is susceptible to
catastrophic backtracking. An attacker could possibly use this issue to
cause a denial of service. (CVE-2021-3842, CVE-2021-43854)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.04 LTS
  python3-nltk                    3.4.5-2ubuntu0.1~esm2
                                  Available with Ubuntu Pro

Ubuntu 18.04 LTS
  python-nltk                     3.2.5-1ubuntu0.1+esm2
                                  Available with Ubuntu Pro
  python3-nltk                    3.2.5-1ubuntu0.1+esm2
                                  Available with Ubuntu Pro

Ubuntu 16.04 LTS
  python-nltk                     3.1-1ubuntu0.1+esm2
                                  Available with Ubuntu Pro
  python3-nltk                    3.1-1ubuntu0.1+esm2
                                  Available with Ubuntu Pro

Ubuntu 14.04 LTS
  python-nltk                     2.0~b9-0ubuntu4.1~esm4
                                  Available with Ubuntu Pro

In general, a standard system update will make all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-7365-1
  CVE-2021-3842, CVE-2021-43854