Answer in brief
CVE-2026-72818 records a High severity (CVSS 8.7) vulnerability in NLTK TweetTokenizer URL Pattern Backtracks Catastrophically on Naked-Domain-Like Input. The current sources do not mark it as known exploited. The current feed maps nltk/nltk (generic), nltk (pip), nltk (pypi). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 8.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps nltk/nltk (generic), nltk (pip), nltk (pypi). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| nltk/nltkgeneric | >=0 <3.10.1 | 3.10.1 |
| nltkpip | <3.10.1 | 3.10.1 |
| nltkpypi | >=0 <3.10.1 | 3.10.1 |
Published upstream
Aug 20, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 24, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 20, 2026
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.
Quoted source text, attributed separately from HOL analysis.