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-2026-63311

CVE-2026-63311MEDIUM

NLTK before 3.10.0 SSRF via DNS Resolution Failure

  AV  AC  AT  PR  UI  VC  VI  VA   CVSS    EPSS   %ile   KEV
   N   L   N   N   N   N   L   N    6.9   .0033   24.5     —

AFFECTED
  Product  Versions     Fixed
  nltk     unspecified  3.10.0

TIMELINE
  Jul 16  Reserved by VulnCheck
  Aug 22  Published (CNA: VulnCheck)
  Aug 27  EXPLOIT PUBLISHED — CVE-2026-63311 (nltk). Public exploit reference added.

CWE-918 · CNA: VulnCheck · CVSS v4.0 · 2 references · NVD status: Analyzed

Description

NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function in nltk/pathsec.py. The _resolve_hostname() helper catches OSError and ValueError during socket.getaddrinfo() and returns an empty list; when DNS resolution fails, the validation loop executes no IP checks and the function fails open, allowing urlopen() to proceed without validation. An attacker who can trigger DNS resolution failures or use DNS rebinding can bypass SSRF protections and reach restricted network resources, including cloud metadata endpoints (e.g., 169.254.169.254).

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
July 16, 2026	Reserved	Reserved by VulnCheck
August 22, 2026	Published	Published (CNA: VulnCheck)
August 27, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-63311 (nltk). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
nltk	nltk	—	—	3.10.0

Weaknesses

CWE-918

References (2)

https://github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839 [Exploit, Mitigation, Vendor Advisory]
https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure [Third Party Advisory]

Authoritative record: CVE-2026-63311 at cve.org

Vendors: nltk

Weaknesses: CWE-918

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-63311 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.