CVE-2026-12259

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

Score 5.3 from GitHub Security Advisory published 2026-08-03. A secondary CVSS source baseline 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.1%CVSS: 5.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

In nltk version 3.9.4, the nltk.downloader.Downloader._download_package() function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for info.url through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.

CVSS v3
5.3
EG Score
5.3MEDIUMmedium confidence
EG Risk
24
EG Risk 24/100CISA 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
Severity53% × 45%
Exploitation0% × 40%
Automatability0% × 15%
CISA SSVC: Track at every mission impact level.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.1%
EPSS %ILE
2nd
KEV
Not listed

CISA SSVCTrack at every mission impact level.

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

Exploitation none (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 3, 2026

Last Modified

August 31, 2026

References (1)

Vendor Advisories for CVE-2026-12259(1)

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

Affected Packages

(5 across 5 ecosystems)
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
nltk3.10.0-1 ... 3.9.3-1 (12 versions)
  • every version on: no fix on record
—
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 (63 versions)
  • every version up to 3.9.3: fixed in 3.9.3
—

Weakness Classification(1)

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

Data Freshness Timeline

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

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-12259?
CVE-2026-12259 is a medium vulnerability published on August 3, 2026. In nltk version 3.9.4, the nltk.downloader.Downloader.downloadpackage() function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for info.url through a compromised…
When was CVE-2026-12259 disclosed?
CVE-2026-12259 was first published on August 3, 2026, with the most recent update on August 31, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-12259 actively exploited?
CVE-2026-12259 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.1% probability of exploitation in the next 30 days (2nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-12259?
CVE-2026-12259 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-2026-12259?
A fix for CVE-2026-12259 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-12259 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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