Unchecked Input for Loop Condition Affecting nltk package, versions [,3.10.3)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-NLTK-19639020
- published7 Sept 2026
- disclosed27 Aug 2026
- creditJoshgunAbdullayev
Introduced: 27 Aug 2026
NewCVE-2026-81724 (opens in a new tab)How to fix?
Upgrade nltk to version 3.10.3 or higher.
Overview
nltk is a Natural Language Toolkit (NLTK) is a Python package for natural language processing.
Affected versions of this package are vulnerable to Unchecked Input for Loop Condition via the FeatStructReader in nltk/featstruct.py. An attacker can trigger an unhandled RecursionError and crash parsing code by supplying a deeply nested feature-structure string to FeatStruct(s), FeatStructReader().fromstring(s), or FeatureGrammar.fromstring(s). The parser’s mutually recursive value-reading path has no nesting-depth limit, so each additional nested [...], {...}, or (...) pushes another Python stack frame until the interpreter’s recursion limit is exceeded. Applications that accept untrusted feature-structure or feature-grammar text can be taken down with a small crafted input, causing denial of service.