{"cve":"CVE-2026-72818","nvd":{"published":"2026-08-20T22:18:05.087","modified":"2026-10-26T10:10:00.140","status":"Awaiting Analysis","description":"The URLS regular expression in nltk/tokenize/casual.py, compiled into TweetTokenizer.WORD_RE and applied by TweetTokenizer.tokenize, contains a naked-domain branch whose domain-label prefix [a-z0-9]+(?:[.\\-][a-z0-9]+)* is unbounded. Input consisting of many alternating label separators can be partitioned in exponentially many ways, and because the branch also requires a trailing top-level domain that such input never supplies, the engine explores those partitions before failing at each offset. A few kilobytes of input therefore consumes seconds to minutes of single-threaded CPU, and the HANG_RE substitution performed before matching does not collapse the pattern. TweetTokenizer is intended for tokenizing untrusted social-media text, so any service that applies it, or the module-level casual_tokenize, to submitted text can be stalled per request without authentication. Version 3.10.1 bounds the label repetition.","cvss_v4":{"vector":"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","score":8.7},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-1333"],"references":["https://github.com/nltk/nltk","https://github.com/nltk/nltk/blob/3.9.4/nltk/tokenize/casual.py","https://github.com/nltk/nltk/issues/3704","https://github.com/nltk/nltk/releases/tag/v3.10.1","https://www.vulncheck.com/advisories/nltk-tweettokenizer-url-pattern-backtracks-catastrophically-on-naked-domain-like-input"],"products":[],"source":"nvd","synced_at":"2026-10-26T10:28:23.151169805+00:00"},"epss":{"cve":"CVE-2026-72818","score":0.00742,"percentile":0.54398,"date":"2026-10-26"},"kev":null,"osv":[{"id":"GHSA-qx2g-xrx7-vfh8","url":"https://osv.dev/vulnerability/GHSA-qx2g-xrx7-vfh8","summary":" NLTK TweetTokenizer vulnerable to denial of service through catastrophic regex backtracking","modified":"2026-09-10T12:25:44.300334208Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.1"],"fixed":["3.10.1"]}]},{"id":"PYSEC-2026-3870","url":"https://osv.dev/vulnerability/PYSEC-2026-3870","summary":" NLTK TweetTokenizer vulnerable to denial of service through catastrophic regex backtracking","modified":"2026-09-10T12:15:10.108062006Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.1"],"fixed":["3.10.1"]}]}],"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."]}