CVE-2026-72818
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.
- Affected products
- Nltk
- CVSS 4.0
- 8.7 HIGH
- CVSS 3.1
- 7.5 HIGH
- EPSS
- 0.5% (41th percentile)
- Weakness
- CWE-1333
- NVD status
- Received
- Published
- 2026-08-20
No indexed exploits for CVE-2026-72818 yet
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