CVE catalog

CVE-2026-12259

Severity: Critical · CVSS 9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published: Aug 3, 2026, 7:09:35 AM UTC
Source: [NVD] · [CVE record]
EPSS: 0.10% · Oct 27, 2026

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.

Vulnerable and fixed packages

Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.

Distribution	Package	Release	Version	Status
Debian	nltk	sid	`3.10.3-1`	vulnerable
Debian	nltk	forky	`3.10.3-1`	vulnerable
Debian	nltk	trixie	`3.9.1-2`	vulnerable
Debian	nltk	bookworm	`3.8-1`	vulnerable
Pip	nltk	Not reported	`3.9.3`	fixed
Cpe	nltk	Not reported	Not reported	unknown
PyPI	nltk	Not reported	`0.8`	vulnerable
PyPI	nltk	Not reported	`0.9`	vulnerable
PyPI	nltk	Not reported	`0.9.3`	vulnerable
PyPI	nltk	Not reported	`0.9.4`	vulnerable
PyPI	nltk	Not reported	`0.9.5`	vulnerable
PyPI	nltk	Not reported	`0.9.6`	vulnerable
PyPI	nltk	Not reported	`0.9.7`	vulnerable
PyPI	nltk	Not reported	`0.9.8`	vulnerable
PyPI	nltk	Not reported	`0.9.9`	vulnerable
PyPI	nltk	Not reported	`2.0.1`	vulnerable
PyPI	nltk	Not reported	`2.0.1rc1`	vulnerable
PyPI	nltk	Not reported	`2.0.1rc2-git`	vulnerable
PyPI	nltk	Not reported	`2.0.1rc3`	vulnerable
PyPI	nltk	Not reported	`2.0.1rc4`	vulnerable
PyPI	nltk	Not reported	`2.0.2`	vulnerable
PyPI	nltk	Not reported	`2.0.3`	vulnerable
PyPI	nltk	Not reported	`2.0.4`	vulnerable
PyPI	nltk	Not reported	`2.0.5`	vulnerable
PyPI	nltk	Not reported	`2.0b4`	vulnerable
PyPI	nltk	Not reported	`2.0b5`	vulnerable
PyPI	nltk	Not reported	`2.0b6`	vulnerable
PyPI	nltk	Not reported	`2.0b7`	vulnerable
PyPI	nltk	Not reported	`2.0b8`	vulnerable
PyPI	nltk	Not reported	`2.0b9`	vulnerable
PyPI	nltk	Not reported	`3.0.0`	vulnerable
PyPI	nltk	Not reported	`3.0.0b1`	vulnerable
PyPI	nltk	Not reported	`3.0.0b2`	vulnerable
PyPI	nltk	Not reported	`3.0.1`	vulnerable
PyPI	nltk	Not reported	`3.0.2`	vulnerable
PyPI	nltk	Not reported	`3.0.3`	vulnerable
PyPI	nltk	Not reported	`3.0.4`	vulnerable
PyPI	nltk	Not reported	`3.0.5`	vulnerable
PyPI	nltk	Not reported	`3.1`	vulnerable
PyPI	nltk	Not reported	`3.2`	vulnerable
PyPI	nltk	Not reported	`3.2.1`	vulnerable
PyPI	nltk	Not reported	`3.2.2`	vulnerable
PyPI	nltk	Not reported	`3.2.3`	vulnerable
PyPI	nltk	Not reported	`3.2.4`	vulnerable
PyPI	nltk	Not reported	`3.2.5`	vulnerable
PyPI	nltk	Not reported	`3.3`	vulnerable
PyPI	nltk	Not reported	`3.4`	vulnerable
PyPI	nltk	Not reported	`3.4.1`	vulnerable
PyPI	nltk	Not reported	`3.4.2`	vulnerable
PyPI	nltk	Not reported	`3.4.3`	vulnerable
PyPI	nltk	Not reported	`3.4.4`	vulnerable
PyPI	nltk	Not reported	`3.4.5`	vulnerable
PyPI	nltk	Not reported	`3.5`	vulnerable
PyPI	nltk	Not reported	`3.5b1`	vulnerable
PyPI	nltk	Not reported	`3.6`	vulnerable
PyPI	nltk	Not reported	`3.6.1`	vulnerable
PyPI	nltk	Not reported	`3.6.2`	vulnerable
PyPI	nltk	Not reported	`3.6.3`	vulnerable
PyPI	nltk	Not reported	`3.6.4`	vulnerable
PyPI	nltk	Not reported	`3.6.5`	vulnerable
PyPI	nltk	Not reported	`3.6.6`	vulnerable
PyPI	nltk	Not reported	`3.6.7`	vulnerable
PyPI	nltk	Not reported	`3.7`	vulnerable
PyPI	nltk	Not reported	`3.8`	vulnerable
PyPI	nltk	Not reported	`3.8.1`	vulnerable
PyPI	nltk	Not reported	`3.9`	vulnerable
PyPI	nltk	Not reported	`3.9.1`	vulnerable
PyPI	nltk	Not reported	`3.9.2`	vulnerable
PyPI	nltk	Not reported	`3.9.3`	vulnerable
PyPI	nltk	Not reported	`3.9.4`	vulnerable
PyPI	nltk	Not reported	`3.9b1`	vulnerable

Fixed-version evidence

Distribution	Package	Type	Release	Fixed version	Urgency	Origin	Bugs
Debian	nltk	source	sid	`(unfixed)`	not yet assigned	Not reported	[1144456]
Debian	nltk	source	forky	`(unfixed)`	not yet assigned	Not reported	[1144456]
Debian	nltk	source	trixie	`(unfixed)`	not yet assigned	Not reported	[1144456]
Debian	nltk	source	bookworm	`(unfixed)`	not yet assigned	Not reported	[1144456]
Pip	nltk	pip	Not reported	`3.9.3`	Not reported	GHSA-5WP5-5229-5G6Q	Not reported

[Debian bug #1144456]

Notes

[trixie] nltk: Minor issue [bookworm] nltk: Minor issue

OpenFactory catalog packages

[Debian 12 (Bookworm)]

[python3-nltk]Affected
Source package: [nltk]
Details (2)
- 3.8-1 · all · bookworm
  Affected
  nvd · nltk · debian · bookworm; nvd · nltk · debian · 12
- 3.8-1 · all · bookworm
  Affected
  nvd · nltk · debian · bookworm; nvd · nltk · debian · 12

[Debian 13 (Trixie)]

[python3-nltk]Affected
Source package: [nltk]
Details (2)
- 3.9.1-2 · all · trixie
  Affected
  nvd · nltk · debian · 13
- 3.9.1-2 · all · trixie
  Affected
  nvd · nltk · debian · 13

Observed: Oct 25, 2026, 7:27:09 AM UTC

References

[Debian Security Tracker] · [FIRST EPSS] · [GitHub Advisory Database] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX]