# CVE-2026-63310

## Summary

- **CVE ID:** CVE-2026-63310
- **Severity:** CRITICAL
- **CVSS Score:** 9.3 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N)
- **CWE:** CWE-494
- **Published:** Aug 22, 2026
- **Last Modified:** Aug 24, 2026

## Description

NLTK before 3.9.3 fails to verify file integrity after downloading packages and before extraction in the downloader module. Attackers can perform man-in-the-middle attacks or DNS poisoning to inject malicious package contents that are extracted without validation.

## Affected Products

- nltk — nltk (0)
- nltk — nltk (3.9.3)

## References

- [CNA](https://github.com/nltk/nltk/security/advisories/GHSA-5wp5-5229-5g6q)
- [CNA](https://www.vulncheck.com/advisories/nltk-before-missing-post-download-integrity-verification)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.12%
- **EPSS Percentile:** 1.8

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