{"answers":{"affected":"3 open source packages ship an affected version, including nltk. It affects 1 product.","exploited":"There is no known exploitation of CVE-2021-43854 in the wild and no public exploit code.","fix":"Upgrade nltk to a fixed version for your release line: 3.6.5 or 3.6.6.","what":"CVE-2021-43854 is a high-severity denial of service vulnerability in nltk, published on 23 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2021-43854 and fix it if it is affected.\n\nWhat it is: CVE-2021-43854 is a high-severity denial of service vulnerability in nltk, published on 23 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2021-43854 in the wild and no public exploit code.\n\nAffected packages and fixed versions:\n- nltk (PyPI): affected all versions; fixed in 3.6.5\n- nltk (PyPI): affected all versions; fixed in 3.6.6\n- nltk (PyPI): affected all versions; fixed in 3.6.6\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2021-43854/ (Markdown: https://insights.sbomify.com/CVE-2021-43854/index.md)","id":"CVE-2021-43854","markdown":"https://insights.sbomify.com/CVE-2021-43854/index.md","name":"CVE-2021-43854","record":{"aliases":["DEBIAN-CVE-2021-43854","GHSA-f8m6-h2c7-8h9x","PYSEC-2021-859","UBUNTU-CVE-2021-43854"],"analysis":{"component_type":"library","fix_type":"upgrade","impacts":["denial_of_service"],"network_reachable":"yes","non_default_config":false,"product_category":"Python NLP library","requires_auth":"none","summary":"Attackers can cause denial of service in NLTK applications by submitting crafted long inputs to tokenization functions, leading to excessive CPU consumption.","user_interaction":"not_required","vuln_class":"denial_of_service"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"GitHub_M","cpe":[{"product":"nltk","vendor":"nltk"}],"cvss":{"score":7.5,"severity":"high","source":"cna","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"},"cwes":[{"id":"CWE-400","name":"Uncontrolled Resource Consumption"}],"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.","ecosystems":["PyPI"],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"Inefficient Regular Expression Complexity in nltk","id":"CVE-2021-43854","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":"PyPI","product":null,"products":[],"type":"denial_of_service","year":"2021"},"n_packages":3,"n_references":4,"next":{"headline":"Stored XSS via SVG in Requarks/wiki","id":"CVE-2021-43855"},"packages":[{"ecosystem":"PyPI","fixed":["3.6.5"],"introduced":["0"],"last_affected":[],"package":"nltk","purl":"pkg:pypi/nltk","source":"PYSEC-2021-859"},{"ecosystem":"PyPI","fixed":["3.6.6"],"introduced":["0"],"last_affected":[],"package":"nltk","purl":null,"source":"GHSA-f8m6-h2c7-8h9x"},{"ecosystem":"PyPI","fixed":["3.6.6"],"introduced":["0"],"last_affected":[],"package":"nltk","purl":"pkg:pypi/nltk","source":"GHSA-f8m6-h2c7-8h9x"}],"prev":{"headline":"Cross-Site Scripting in AjaxNetProfessional","id":"CVE-2021-43853"},"products":["nltk"],"published":"2021-12-23","related":[{"cvss_score":10,"headline":"Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading","id":"CVE-2026-0848","kev_date_added":null,"published":"2026-03-05"},{"cvss_score":10,"headline":"Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution","id":"CVE-2025-14009","kev_date_added":null,"published":"2026-02-18"},{"cvss_score":9.4,"headline":"NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization","id":"CVE-2026-78683","kev_date_added":null,"published":"2026-08-25"},{"cvss_score":9.3,"headline":"NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization","id":"CVE-2026-79657","kev_date_added":null,"published":"2026-08-25"},{"cvss_score":9.3,"headline":"NLTK before 3.10.3 JVM Argument Injection via Per-Call Options","id":"CVE-2026-79675","kev_date_added":null,"published":"2026-08-25"},{"cvss_score":8.8,"headline":"NLTK 3.10.2 Path Traversal via corpus-reader constructors","id":"CVE-2026-79674","kev_date_added":null,"published":"2026-08-25"},{"cvss_score":8.7,"headline":"nltk PorterStemmer before 3.10.3 Quadratic-time DoS","id":"CVE-2026-81722","kev_date_added":null,"published":"2026-08-27"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"CC BY 4.0","name":"GitHub Advisory Database","prefix":"GHSA"},{"class":"attribution","licence":"CC BY 4.0","name":"PyPA Advisory Database","prefix":"PYSEC"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":null,"exploitation":null,"technical_impact":null},"state":"PUBLISHED","updated":"2024-08-04","vendors":["nltk"]},"summary":"Attackers can cause denial of service in NLTK applications by submitting crafted long inputs to tokenization functions, leading to excessive CPU consumption.","url":"https://insights.sbomify.com/CVE-2021-43854/"}