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.
Metrics
Affected Vendors & Products
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History
Fri, 21 Aug 2026 11:30:00 +0000
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ssvc
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Thu, 20 Aug 2026 22:15:00 +0000
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| 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. | |
| Title | NLTK TweetTokenizer URL Pattern Backtracks Catastrophically on Naked-Domain-Like Input | |
| First Time appeared |
Nltk
Nltk nltk |
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| Weaknesses | CWE-1333 | |
| CPEs | cpe:2.3:a:nltk:nltk:3.6.5:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.6.6:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.6.7:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.7:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.8.1:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.8:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.9.1:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.9.2:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.9.3:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.9:*:*:*:*:*:*:* cpe:2.3:a:nltk:nltk:3.9:beta1:*:*:*:*:*:* |
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Nltk
Nltk nltk |
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cvssV3_1
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Status: PUBLISHED
Assigner: VulnCheck
Published:
Updated: 2026-08-21T11:20:57.674Z
Reserved: 2026-08-10T15:12:16.754Z
Link: CVE-2026-72818
Updated: 2026-08-21T11:06:02.698Z
Status : Received
Published: 2026-08-20T22:18:05.087
Modified: 2026-08-21T11:17:05.920
Link: CVE-2026-72818
No data.
OpenCVE Enrichment
Updated: 2026-08-21T01:15:06Z