CVE-2026-80206NLTK 3.10.2 Regular Expression Denial of Service via tgrep

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.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• GitHub Security Advisory (GHSA-w3v8-gmh9-3wv7) vendor-advisoryExploitVendor Advisory
• VulnCheck Advisory: NLTK 3.10.2 Regular Expression Denial of Service via tgrep third-party-advisoryThird Party Advisory