{"cve":"CVE-2026-78683","nvd":{"published":"2026-08-25T02:16:53.033","modified":"2026-10-12T17:10:00.163","status":"Analyzed","description":"NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H","score":9.4},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H","score":9.6},"cwes":["CWE-502"],"references":["https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2","https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization","https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-78683","score":0.0051,"percentile":0.43255,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-rhp5-r9x4-f5g2","url":"https://osv.dev/vulnerability/GHSA-rhp5-r9x4-f5g2","summary":"NLTK: Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution","modified":"2026-09-08T16:45:04.193165862Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.0"],"fixed":["3.10.0"]}]},{"id":"PYSEC-2026-3734","url":"https://osv.dev/vulnerability/PYSEC-2026-3734","summary":"","modified":"2026-09-01T09:15:02.843391088Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.0"],"fixed":["3.10.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}