Duplicate Advisory: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions
GHSA-vf76-f5cp-9846
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Description
Duplicate Advisory
This advisory has been withdrawn because it is a duplicate of GHSA-w3v8-gmh9-3wv7. This link is maintained to preserve external references.
Original Description
NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.
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