CVE-2026-63311

MEDIUMPre-NVD 5.35.3
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

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, GitHub Security Advisory, a secondary CVSS source
5.3EG
EchelonGraph verdictMonitorRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 5.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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
5.3MEDIUMmedium confidence
EG Risk
39
EG Risk 39/100

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 (value × EchelonGraph’s weight)
Severity53% × 45%
The EG Score, 5.3 of 10.
Exploitation0.3% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.3%
EPSS %ILE
25th
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

August 22, 2026

Last Modified

October 14, 2026

Advisory Details (2)

Auto-updated Aug 22, 2026
Patch available. Sources: github.
Web page

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 advisoryMentions a patch (unverified)

[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

(4 across 4 ecosystems)
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
nltk3.10.0-1 ... 3.9.3-1 (9 versions)
  • every version on: no fix on record
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
nltk3.10.0-1 ... 3.9.3-1 (6 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
nltk3.9.1-2, 3.9.2-1, 3.9.3-1
  • every version up to 3.10.0-1: fixed in 3.10.0-1
—
PyPI(1)
PackageVulnerable rangeFix by version rangeDependents
nltk0.8 ... 3.9b1 (65 versions)
  • every version up to 3.10.0: fixed in 3.10.0
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 15× in last 7d / 48× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-10-14 13:36 UTCEG score recompute
  2. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  3. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  4. 2026-10-12 15:49 UTCEG score recompute
  5. 2026-10-11 19:33 UTCEG score recompute
  6. 2026-10-11 16:48 UTCEG score recompute
  7. 2026-10-11 14:10 UTCEG score recompute
  8. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  9. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  10. 2026-10-10 16:35 UTCEG score recompute
  11. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  12. 2026-10-09 05:43 UTCEG score recompute
  13. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  14. 2026-10-08 04:48 UTCEG score recompute
  15. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  16. 2026-10-07 03:55 UTCEG score recompute
  17. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  18. 2026-10-06 03:01 UTCEG score recompute
  19. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  20. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  21. 2026-10-03 16:39 UTCEG score recompute
  22. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  23. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  24. 2026-10-02 09:20 UTCEG score recompute
  25. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.3% · 24th percentile
Show 74 more
  1. 2026-10-01 08:26 UTCEG score recompute
  2. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  3. 2026-09-30 07:33 UTCEG score recompute
  4. 2026-09-29 02:55 UTCEG score recompute
  5. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  6. 2026-09-28 02:01 UTCEG score recompute
  7. 2026-09-27 01:08 UTCEG score recompute
  8. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  9. 2026-09-24 17:09 UTCEG score recompute
  10. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  11. 2026-09-23 16:15 UTCEG score recompute
  12. 2026-09-22 15:22 UTCEG score recompute
  13. 2026-09-21 14:28 UTCEG score recompute
  14. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  15. 2026-09-20 13:28 UTCEG score recompute
  16. 2026-09-19 12:14 UTCEG score recompute
  17. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  18. 2026-09-18 11:21 UTCEG score recompute
  19. 2026-09-17 10:27 UTCEG score recompute
  20. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  21. 2026-09-16 09:33 UTCEG score recompute
  22. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  23. 2026-09-15 07:04 UTCEG score recompute
  24. 2026-09-14 06:10 UTCEG score recompute
  25. 2026-09-13 05:17 UTCEG score recompute
  26. 2026-09-12 04:23 UTCEG score recompute
  27. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  28. 2026-09-11 09:37 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  29. 2026-09-11 03:29 UTCEG score recompute
  30. 2026-09-09 01:42 UTCEG score recompute
  31. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  32. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  33. 2026-09-07 09:58 UTCEG score recompute
  34. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  35. 2026-09-06 08:57 UTCEG score recompute
  36. 2026-09-05 15:31 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  37. 2026-09-05 08:04 UTCEG score recompute
  38. 2026-09-04 07:11 UTCEG score recompute
  39. 2026-09-04 05:07 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  40. 2026-09-03 05:52 UTCEG score recompute
  41. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  42. 2026-09-02 04:59 UTCEG score recompute
  43. 2026-09-02 04:58 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  44. 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  45. 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  46. 2026-09-01 04:04 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  47. 2026-08-31 02:48 UTCEG score recompute
  48. 2026-08-31 02:48 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  49. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  50. 2026-08-30 01:54 UTCEG score recompute
  51. 2026-08-30 01:53 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  52. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  53. 2026-08-29 01:00 UTCEG score recompute
  54. 2026-08-29 01:00 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  55. 2026-08-28 21:42 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  56. 2026-08-27 19:46 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  57. 2026-08-27 18:24 UTCEG score recompute
  58. 2026-08-27 18:24 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  59. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.2% · 16th percentile
  60. 2026-08-26 17:25 UTCEG score recompute
  61. 2026-08-26 17:25 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  62. 2026-08-26 16:23 UTCEG score recompute
  63. 2026-08-26 16:23 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  64. 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.2% · 16th percentile
  65. 2026-08-25 18:07 UTCEG score recompute
  66. 2026-08-25 18:07 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  67. 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  68. 2026-08-24 17:11 UTCEG score recompute
  69. 2026-08-24 17:11 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  70. 2026-08-23 16:17 UTCEG score recompute
  71. 2026-08-23 16:17 UTCGHSA enrichmentGHSA-qg9p-xrhj-435m · GitHub CVSS 5.3
  72. 2026-08-22 15:24 UTCEG score recompute
  73. 2026-08-22 14:26 UTCEG score recomputeFirst assessed: 5.3 MEDIUM
  74. 2026-08-22 14:25 UTCMITRE cvelistV5first tracked

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-63311?
CVE-2026-63311 is a medium-severity vulnerability; its CVE record was 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 made public?
CVE-2026-63311 was made public on August 7, 2026: that is the date its CVE record's CNA, VulnCheck, gives for when the vulnerability was made public. The CVE record itself was published on August 22, 2026. EchelonGraph's copy of the record carries a last-modified date of October 14, 2026; the record at its source may have been updated since.
Is CVE-2026-63311 actively exploited?
CVE-2026-63311 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (25th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-63311?
CVE-2026-63311 has a CVSS base score of 5.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-63311?
A fix for CVE-2026-63311 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-63311 are linked in the Vendor Advisories panel on this page.

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