CVE-2026-66393

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-08-22. A secondary CVSS source baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Elevated
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.5%CVSS: 7.5Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.decode_obj() that allows attackers to cause denial of service by supplying deeply nested JSON structures. Attackers can craft JSON payloads exceeding the recursion limit to trigger an unhandled RecursionError that crashes the Python process.

CVSS v3
7.5
EG Score
7.5HIGHmedium confidence
EG Risk
65
EG Risk 65/100CISA SSVC

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
Severity75% × 45%
Exploitation40% × 40%
Automatability100% × 15%
CISA SSVC: Track at low or medium mission impact; Attend at high (mission-essential systems).
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
0.5%
EPSS %ILE
42nd
KEV
Not listed

CISA SSVCTrack 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 public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

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 3.9.4 Denial of Service via JSONTaggedDecoder | Advisories | VulnCheck

https://www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecoder
githubMentions a patch (unverified)🟡 PoC Available

Unbounded recursion in JSONTaggedDecoder.decode_obj() may cause DoS · Advisory · nltk/nltk · GitHub

https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw

Vendor Advisories for CVE-2026-66393(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 (64 versions)
  • every version up to 3.9.4: fixed in 3.9.4
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 13× in last 7d / 49× 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.

Showing the most recent 100 of 108 total refreshes for this CVE.

  1. 2026-10-10 20:00 UTCEPSS rescore
  2. 2026-10-10 16:35 UTCEG score recompute
  3. 2026-10-09 20:07 UTCEPSS rescore
  4. 2026-10-09 05:33 UTCEG score recompute
  5. 2026-10-08 17:13 UTCEPSS rescore
  6. 2026-10-08 04:42 UTCEG score recompute
  7. 2026-10-07 23:48 UTCEPSS rescore
  8. 2026-10-06 16:48 UTCEG score recompute
  9. 2026-10-06 15:18 UTCEPSS rescore
  10. 2026-10-06 03:01 UTCEG score recompute
  11. 2026-10-05 17:43 UTCEPSS rescore
  12. 2026-10-05 09:25 UTCEG score recompute
  13. 2026-10-04 23:22 UTCEPSS rescore
  14. 2026-10-03 16:38 UTCEG score recompute
  15. 2026-10-03 14:26 UTCEPSS rescore
  16. 2026-10-02 22:14 UTCEG score recompute
  17. 2026-10-02 17:56 UTCEPSS rescore
  18. 2026-10-01 21:23 UTCEG score recompute
  19. 2026-10-01 19:50 UTCEPSS rescore
  20. 2026-09-30 20:22 UTCEG score recompute
  21. 2026-09-30 15:03 UTCEPSS rescore
  22. 2026-09-30 07:33 UTCEG score recompute
  23. 2026-09-29 04:22 UTCEG score recompute
  24. 2026-09-28 15:56 UTCEG score recompute
  25. 2026-09-28 13:52 UTCEPSS rescore
Show 75 more
  1. 2026-09-27 14:38 UTCEG score recompute
  2. 2026-09-27 01:08 UTCEG score recompute
  3. 2026-09-26 15:59 UTCEPSS rescore
  4. 2026-09-24 22:22 UTCEG score recompute
  5. 2026-09-23 20:32 UTCEG score recompute
  6. 2026-09-23 17:54 UTCEPSS rescore
  7. 2026-09-22 19:42 UTCEG score recompute
  8. 2026-09-22 03:47 UTCEG score recompute
  9. 2026-09-21 02:38 UTCEG score recompute
  10. 2026-09-20 20:16 UTCEPSS rescore
  11. 2026-09-20 01:47 UTCEG score recompute
  12. 2026-09-19 00:57 UTCEG score recompute
  13. 2026-09-18 19:28 UTCEPSS rescore
  14. 2026-09-18 00:06 UTCEG score recompute
  15. 2026-09-16 21:59 UTCEG score recompute
  16. 2026-09-16 14:08 UTCEPSS rescore
  17. 2026-09-16 09:34 UTCEG score recompute
  18. 2026-09-16 05:15 UTCEPSS rescore
  19. 2026-09-15 07:31 UTCEG score recompute
  20. 2026-09-13 17:38 UTCEG score recompute
  21. 2026-09-12 16:48 UTCEG score recompute
  22. 2026-09-11 15:54 UTCEG score recompute
  23. 2026-09-11 14:53 UTCEPSS rescore
  24. 2026-09-11 09:37 UTCEPSS rescore
  25. 2026-09-10 15:04 UTCEG score recompute
  26. 2026-09-09 01:42 UTCEG score recompute
  27. 2026-09-08 22:01 UTCEPSS rescore
  28. 2026-09-08 03:52 UTCEG score recompute
  29. 2026-09-07 16:01 UTCEPSS rescore
  30. 2026-09-07 01:37 UTCEG score recompute
  31. 2026-09-06 13:47 UTCEPSS rescore
  32. 2026-09-06 00:42 UTCEG score recompute
  33. 2026-09-05 15:31 UTCEPSS rescore
  34. 2026-09-04 23:47 UTCEG score recompute
  35. 2026-09-04 10:51 UTCEG score recompute
  36. 2026-09-04 05:07 UTCEPSS rescore
  37. 2026-09-02 21:29 UTCEG score recompute
  38. 2026-09-02 14:12 UTCEPSS rescore
  39. 2026-09-02 09:02 UTCGHSA enrichment
  40. 2026-09-01 20:31 UTCEG score recompute
  41. 2026-09-01 20:31 UTCGHSA enrichment
  42. 2026-09-01 13:54 UTCEPSS rescore
  43. 2026-09-01 08:06 UTCEG score recompute
  44. 2026-09-01 08:05 UTCGHSA enrichment
  45. 2026-09-01 04:40 UTCEPSS rescore
  46. 2026-08-31 19:36 UTCGHSA enrichment
  47. 2026-08-31 06:52 UTCEG score recompute
  48. 2026-08-31 06:52 UTCGHSA enrichment
  49. 2026-08-30 19:17 UTCEPSS rescore
  50. 2026-08-30 18:27 UTCGHSA enrichment
  51. 2026-08-30 06:02 UTCEG score recompute
  52. 2026-08-30 06:02 UTCGHSA enrichment
  53. 2026-08-30 01:22 UTCEPSS rescore
  54. 2026-08-29 17:36 UTCGHSA enrichment
  55. 2026-08-29 04:59 UTCEG score recompute
  56. 2026-08-29 04:59 UTCGHSA enrichment
  57. 2026-08-28 21:42 UTCEPSS rescore
  58. 2026-08-28 16:30 UTCGHSA enrichment
  59. 2026-08-28 03:23 UTCGHSA enrichment
  60. 2026-08-27 14:58 UTCEG score recompute
  61. 2026-08-27 14:58 UTCGHSA enrichment
  62. 2026-08-27 06:50 UTCGHSA enrichment
  63. 2026-08-26 18:24 UTCEG score recompute
  64. 2026-08-26 18:24 UTCGHSA enrichment
  65. 2026-08-26 18:04 UTCEG score recompute
  66. 2026-08-26 18:04 UTCGHSA enrichment
  67. 2026-08-26 17:25 UTCEG score recompute
  68. 2026-08-26 17:25 UTCGHSA enrichment
  69. 2026-08-26 14:47 UTCEPSS rescore
  70. 2026-08-26 06:26 UTCGHSA enrichment
  71. 2026-08-25 17:58 UTCEG score recompute
  72. 2026-08-25 17:57 UTCGHSA enrichment
  73. 2026-08-25 13:49 UTCEPSS rescore
  74. 2026-08-25 05:32 UTCGHSA enrichment
  75. 2026-08-24 17:07 UTCEG score recompute

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-66393?
CVE-2026-66393 is a high vulnerability published on August 22, 2026. NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.decode_obj() that allows attackers to cause denial of service by supplying deeply nested JSON structures. Attackers can craft JSON payloads exceeding the recursion limit to trigger an unhandled…
When was CVE-2026-66393 disclosed?
CVE-2026-66393 was first published 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-2026-66393 actively exploited?
CVE-2026-66393 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.5% probability of exploitation in the next 30 days (42nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-66393?
CVE-2026-66393 has a CVSS base score of 7.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-66393?
A fix for CVE-2026-66393 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-66393 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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