{"id":"CVE-2026-72818","summary":"NLTK TweetTokenizer URL Pattern Backtracks Catastrophically on Naked-Domain-Like Input","details":"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.","modified":"2026-08-23T03:42:46.409180706Z","published":"2026-08-20T21:57:34.230Z","database_specific":{"cwe_ids":["CWE-1333"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72818.json","cna_assigner":"VulnCheck"},"references":[{"type":"WEB","url":"https://pypi.org"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72818.json"},{"type":"ADVISORY","url":"https://github.com/nltk/nltk/releases/tag/v3.10.1"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-72818"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/nltk-tweettokenizer-url-pattern-backtracks-catastrophically-on-naked-domain-like-input"},{"type":"REPORT","url":"https://github.com/nltk/nltk/issues/3704"},{"type":"PACKAGE","url":"https://github.com/nltk/nltk"},{"type":"ARTICLE","url":"https://github.com/nltk/nltk/blob/3.9.4/nltk/tokenize/casual.py"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/nltk/nltk","events":[{"introduced":"0"},{"fixed":"35813c85af3f13d4f7196085854eafb3d0c5db02"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"3.10.1"}],"source":["AFFECTED_FIELD","REFERENCES"]}}],"versions":["v3.10.1-rc2","v3.10.0-rc2","v3.10.0","v3.10.1-rc1","v3.10.0-rc1","3.9.4","3.9.3","v3.9.2","3.9.2","3.9.1","3.9","3.8.2","3.8.1","3.8","3.7","3.6.7","3.6.6","3.6.5","3.6.2","3.6.1","3.6","3.5","3.5b1","3.4.4","3.4.3","3.4.1","3.4","3.3","3.2.5","3.2.4","3.2.3","3.2.2","3.2.1","3.2","3.1","3.0.5","3.0.4","3.0.3","3.0.2","3.0.0b1","3.0a4","2.0.1rc4","2.0.1rc3","2.0.1rc2","2.0.1rc1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-72818.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}