CVE-2026-12261

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under NVD CVSS v3. EPSS exploit probability: 0.2% (9th percentile of EPSS-scored CVEs). GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: epss, ghsa, nvd
Trending — 3 sources updated this weekElevated
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 6.5Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

A vulnerability in nltk.downloader in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as corpora/ and taggers/ instead of package-isolated roots, and validates package integrity only after the archive has been written and extracted. This design flaw enables one package to overwrite another package's trusted resources within the same namespace, making the changes immediately active through ordinary NLTK APIs. This issue persists across fresh interpreter restarts and can affect downstream workflows, including machine learning pipelines and reproducibility-sensitive environments.

CVSS v3
6.5
EG Score
6.5MEDIUMmedium confidence
EG Risk
45
EG Risk 45/100CISA 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
Severity65% × 45%
Exploitation40% × 40%
Automatability0% × 15%
CISA SSVC: Track at low or medium mission impact; Track* at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.2%
EPSS %ILE
9th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (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 7, 2026

Last Modified

September 4, 2026

Advisory Details (1)

Auto-updated Aug 7, 2026
Patch available.
generic

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Vendor Advisories for CVE-2026-12261(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
nltk3.10.0-1 ... 3.9.3-1 (6 versions)
  • every version on: no fix on record
—
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 13× in last 7d / 67× 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 151 total refreshes for this CVE.

  1. 2026-10-05 08:17 UTCEG score recompute
  2. 2026-10-04 23:21 UTCEPSS rescore
  3. 2026-10-04 05:45 UTCEG score recompute
  4. 2026-10-03 14:25 UTCEPSS rescore
  5. 2026-10-02 09:34 UTCEG score recompute
  6. 2026-10-02 09:34 UTCGHSA enrichment
  7. 2026-10-01 19:49 UTCEPSS rescore
  8. 2026-09-30 22:57 UTCEG score recompute
  9. 2026-09-30 22:57 UTCGHSA enrichment
  10. 2026-09-30 15:02 UTCEPSS rescore
  11. 2026-09-29 15:20 UTCEPSS rescore
  12. 2026-09-29 05:48 UTCEG score recompute
  13. 2026-09-29 05:48 UTCGHSA enrichment
  14. 2026-09-28 13:50 UTCEPSS rescore
  15. 2026-09-27 17:11 UTCEG score recompute
  16. 2026-09-27 17:11 UTCGHSA enrichment
  17. 2026-09-26 15:58 UTCEPSS rescore
  18. 2026-09-25 04:17 UTCEG score recompute
  19. 2026-09-25 04:17 UTCGHSA enrichment
  20. 2026-09-23 23:36 UTCEG score recompute
  21. 2026-09-23 23:36 UTCGHSA enrichment
  22. 2026-09-23 13:47 UTCEPSS rescore
  23. 2026-09-22 23:57 UTCEG score recompute
  24. 2026-09-22 23:57 UTCGHSA enrichment
  25. 2026-09-22 00:47 UTCEG score recompute
Show 75 more
  1. 2026-09-22 00:47 UTCGHSA enrichment
  2. 2026-09-20 22:51 UTCEG score recompute
  3. 2026-09-20 22:51 UTCGHSA enrichment
  4. 2026-09-20 20:15 UTCEPSS rescore
  5. 2026-09-19 23:14 UTCEG score recompute
  6. 2026-09-19 23:14 UTCGHSA enrichment
  7. 2026-09-18 23:54 UTCEG score recompute
  8. 2026-09-18 23:53 UTCGHSA enrichment
  9. 2026-09-18 19:27 UTCEPSS rescore
  10. 2026-09-18 00:56 UTCEG score recompute
  11. 2026-09-18 00:56 UTCGHSA enrichment
  12. 2026-09-17 01:46 UTCEG score recompute
  13. 2026-09-17 01:46 UTCGHSA enrichment
  14. 2026-09-16 05:14 UTCEPSS rescore
  15. 2026-09-16 02:53 UTCEG score recompute
  16. 2026-09-16 02:53 UTCGHSA enrichment
  17. 2026-09-15 01:01 UTCGHSA enrichment
  18. 2026-09-14 00:28 UTCEG score recompute
  19. 2026-09-14 00:28 UTCGHSA enrichment
  20. 2026-09-13 16:46 UTCEPSS rescore
  21. 2026-09-13 01:35 UTCEG score recompute
  22. 2026-09-13 01:35 UTCGHSA enrichment
  23. 2026-09-12 15:00 UTCEPSS rescore
  24. 2026-09-12 02:41 UTCEG score recompute
  25. 2026-09-12 02:41 UTCGHSA enrichment
  26. 2026-09-11 14:52 UTCEPSS rescore
  27. 2026-09-11 09:36 UTCEPSS rescore
  28. 2026-09-11 03:48 UTCEG score recompute
  29. 2026-09-11 03:48 UTCGHSA enrichment
  30. 2026-09-10 09:34 UTCEPSS rescore
  31. 2026-09-10 04:55 UTCGHSA enrichment
  32. 2026-09-09 06:01 UTCEG score recompute
  33. 2026-09-09 06:01 UTCGHSA enrichment
  34. 2026-09-08 22:00 UTCEPSS rescore
  35. 2026-09-07 17:46 UTCEG score recompute
  36. 2026-09-07 17:46 UTCGHSA enrichment
  37. 2026-09-07 16:01 UTCEPSS rescore
  38. 2026-09-06 15:33 UTCEG score recompute
  39. 2026-09-06 15:33 UTCGHSA enrichment
  40. 2026-09-06 13:47 UTCEPSS rescore
  41. 2026-09-05 16:12 UTCEG score recompute
  42. 2026-09-05 16:12 UTCGHSA enrichment
  43. 2026-09-04 14:49 UTCEG score recompute▲ 1.20
  44. 2026-09-04 14:49 UTCGHSA enrichment
  45. 2026-09-04 14:47 UTCNVD updateCVSS v3 → 6.5
  46. 2026-09-04 09:07 UTCEG score recompute
  47. 2026-09-04 09:07 UTCGHSA enrichment
  48. 2026-09-04 05:06 UTCEPSS rescore
  49. 2026-09-03 06:08 UTCEG score recompute
  50. 2026-09-03 06:08 UTCGHSA enrichment
  51. 2026-09-02 14:11 UTCEPSS rescore
  52. 2026-09-01 18:36 UTCEG score recompute
  53. 2026-09-01 18:35 UTCGHSA enrichment
  54. 2026-09-01 13:53 UTCEPSS rescore
  55. 2026-09-01 04:39 UTCEPSS rescore
  56. 2026-08-31 19:41 UTCGHSA enrichment
  57. 2026-08-31 09:59 UTCEG score recompute
  58. 2026-08-31 09:59 UTCGHSA enrichment
  59. 2026-08-30 19:17 UTCEPSS rescore
  60. 2026-08-30 09:42 UTCEG score recompute
  61. 2026-08-30 09:42 UTCGHSA enrichment
  62. 2026-08-30 01:21 UTCEPSS rescore
  63. 2026-08-29 10:25 UTCEG score recompute
  64. 2026-08-29 10:25 UTCGHSA enrichment
  65. 2026-08-28 21:40 UTCEPSS rescore
  66. 2026-08-27 19:49 UTCEG score recompute
  67. 2026-08-27 19:49 UTCGHSA enrichment
  68. 2026-08-27 14:24 UTCEPSS rescore
  69. 2026-08-26 18:59 UTCEG score recompute
  70. 2026-08-26 18:59 UTCGHSA enrichment
  71. 2026-08-25 19:41 UTCGHSA enrichment
  72. 2026-08-24 20:49 UTCEG score recompute
  73. 2026-08-24 20:49 UTCGHSA enrichment
  74. 2026-08-23 21:56 UTCEG score recompute
  75. 2026-08-23 21:56 UTCGHSA enrichment

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-12261?
CVE-2026-12261 is a medium vulnerability published on August 7, 2026. A vulnerability in nltk.downloader in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as corpora/ and taggers/ instead of package-isolated roots, and validates package integrity only after the…
When was CVE-2026-12261 disclosed?
CVE-2026-12261 was first published on August 7, 2026, with the most recent update on September 4, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-12261 actively exploited?
CVE-2026-12261 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (9th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-12261?
CVE-2026-12261 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-12261?
A fix for CVE-2026-12261 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-12261 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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