CVE-2021-43854
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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
Debian Mixed 5 releases
| Version | Status | Fixed in |
|---|---|---|
| trixie | Fixed | 3.6.7-1 |
| sid | Fixed | 3.6.7-1 |
| forky | Fixed | 3.6.7-1 |
| bullseye | Affected | — |
| bookworm | Fixed | 3.6.7-1 |
References
- https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x
- https://nvd.nist.gov/vuln/detail/CVE-2021-43854
- https://github.com/nltk/nltk/issues/2866
- https://github.com/nltk/nltk/pull/2869
- https://github.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341
- https://github.com/nltk/nltk
- https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2021-859.yaml
- https://security-tracker.debian.org/tracker/CVE-2021-43854
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.