CVE-2026-63311

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreHIGH confidence

Score 5.3 from GitHub Security Advisory published 2026-08-22. a secondary CVSS source baseline 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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).

CVSS v3
5.3
EG Score
5.3(high)
EG Risk
39(Track)
EG Risk 39/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity53% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
15%
KEV
Not listed

Published

August 22, 2026

Last Modified

August 27, 2026

Advisory Details (2)

Auto-updated Aug 22, 2026
🔬 Proof of concept available. Patch available. Sources: github.
generic

NLTK before 3.10.0 SSRF via DNS Resolution Failure | Advisories | VulnCheck

https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure
github Patch Available🟡 PoC Available

[CWE-918] SSRF Fail-Open in validate_network_url() via DNS Resolution Failure · Advisory · nltk/nltk · GitHub

https://github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839

Vendor Advisories for CVE-2026-63311(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
nltk0.8 ... 3.9b1 (65 versions)3.10.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 22× in last 7d / 25× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-08-30 01:54 UTCEG score recompute
  2. 2026-08-30 01:53 UTCGHSA enrichment
  3. 2026-08-30 01:22 UTCEPSS rescore
  4. 2026-08-29 01:00 UTCEG score recompute
  5. 2026-08-29 01:00 UTCGHSA enrichment
  6. 2026-08-28 21:42 UTCEPSS rescore
  7. 2026-08-27 19:46 UTCGHSA enrichment
  8. 2026-08-27 18:24 UTCEG score recompute
  9. 2026-08-27 18:24 UTCGHSA enrichment
  10. 2026-08-27 14:25 UTCEPSS rescore
  11. 2026-08-26 17:25 UTCEG score recompute
  12. 2026-08-26 17:25 UTCGHSA enrichment
  13. 2026-08-26 16:23 UTCEG score recompute
  14. 2026-08-26 16:23 UTCGHSA enrichment
  15. 2026-08-26 14:46 UTCEPSS rescore
  16. 2026-08-25 18:07 UTCEG score recompute
  17. 2026-08-25 18:07 UTCGHSA enrichment
  18. 2026-08-25 13:49 UTCEPSS rescore
  19. 2026-08-24 17:11 UTCEG score recompute
  20. 2026-08-24 17:11 UTCGHSA enrichment
  21. 2026-08-23 16:17 UTCEG score recompute
  22. 2026-08-23 16:17 UTCGHSA enrichment
  23. 2026-08-22 15:24 UTCEG score recompute
  24. 2026-08-22 14:26 UTCEG score recompute
  25. 2026-08-22 14:25 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-63311?
CVE-2026-63311 is a medium vulnerability published on August 22, 2026. NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validatenetworkurl() function in nltk/pathsec.py. The resolvehostname() helper catches OSError and ValueError during socket.getaddrinfo() and returns an empty list; when DNS resolution…
When was CVE-2026-63311 disclosed?
CVE-2026-63311 was first published in the National Vulnerability Database on August 22, 2026, with the most recent update on August 27, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-63311 actively exploited?
CVE-2026-63311 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 84.9% of all scored CVEs.
What is the CVSS score of CVE-2026-63311?
CVE-2026-63311 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-63311?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63311, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-63311

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