Inefficient Regular Expression Complexity Affecting nemo package, versions <2.7.3-r27


Severity

Recommended
0.0
high
0
10

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Threat Intelligence

EPSS
0.74% (53rd percentile)

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  • Snyk IDSNYK-CHAINGUARDLATEST-NEMO-19533667
  • published5 Sept 2026
  • disclosed20 Aug 2026

Introduced: 20 Aug 2026

CVE-2026-72818  (opens in a new tab)
CWE-1333  (opens in a new tab)

How to fix?

Upgrade Chainguard nemo to version 2.7.3-r27 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream nemo package and not the nemo package as distributed by Chainguard. See How to fix? for Chainguard relevant fixed versions and status.

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 Base Scores

version 3.1