Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-80206

CVE-2026-80206HIGH

NLTK 3.10.2 Regular Expression Denial of Service via tgrep

  AV  AC  AT  PR  UI  VC  VI  VA   CVSS    EPSS   %ile   KEV
   N   H   P   N   N   N   N   H    8.2   .0044   36.1     —

AFFECTED
  Product  Versions     Fixed
  nltk     unspecified  3.10.3

TIMELINE
  Aug 25  Reserved by VulnCheck
  Aug 26  Published (CNA: VulnCheck)
  Sep 1   EXPLOIT PUBLISHED — CVE-2026-80206 (nltk). Public exploit reference added.

CWE-1333 · CNA: VulnCheck · CVSS v4.0 · 2 references · NVD status: Analyzed

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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 25, 2026	Reserved	Reserved by VulnCheck
August 26, 2026	Published	Published (CNA: VulnCheck)
September 1, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-80206 (nltk). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
nltk	nltk	—	—	3.10.3

Weaknesses

CWE-1333

References (2)

https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7 [Exploit, Vendor Advisory]
https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep [Third Party Advisory]

Authoritative record: CVE-2026-80206 at cve.org

Vendors: nltk

Weaknesses: CWE-1333

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-80206 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.