# CVE-2026-80206

## Summary

- **CVE ID:** CVE-2026-80206
- **Severity:** HIGH
- **CVSS Score:** 8.2 (CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N)
- **CWE:** CWE-1333
- **Published:** Aug 26, 2026
- **Last Modified:** Aug 26, 2026

## 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.

## Affected Products

- nltk — nltk (0)
- nltk — nltk (3.10.3)

## References

- [CNA](https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7)
- [CNA](https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.26%
- **EPSS Percentile:** 18.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._