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Fencer Vulns
critical 9.6

CVE-2026-78683 json

NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization

published 2026-08-25 2 mo ago modified 2026-10-12 27 d ago also GHSA-rhp5-r9x4-f5g2 , PYSEC-2026-3734 , EUVD-2026-65229

cvss
9.6
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits
0
none known

Summary

NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.

Patch / fix

  • pypi nltk 3.10.0
  • nltk nltk 3.10.0
  • nltk Debian 14 3.10.0-1

debian advisories DEBIAN-CVE-2026-78683

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-78683 updated cvss 9.6

nltk: NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization

  • Red Hat Lightspeed Core lightspeed-core/lightspeed-stack-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-ocp-rag-rhel9, openshift-lightspeed-tech-preview/lightspeed-rag-tool-rhel9
    affected: workaround, no fix available
  • Red Hat Ansible Automation Platform 2 ansible-automation-platform-25/lightspeed-chatbot-rhel8
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift AI 3.4 rhoai/odh-ta-lmes-job-rhel9 1791470318, rhoai/odh-trustyai-garak-lls-provider-dsp-rhel9 1791785804
    fixed: vendor fix RHSA-2026:84734
  • Red Hat Lightspeed Core lightspeed-core/rag-tool-cpu-rhel9, lightspeed-core/rag-tool-cuda-12.9-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-service-api-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-ogx-core-rhel9, rhoai/odh-llama-stack-core-rhel9, rhoai/odh-trustyai-nemo-guardrails-server-rhel9, rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9, rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1791509689, rhoai/rhai-cli-rhel9 1791509689, rhoai/odh-automl-rhel9 1791535789, rhoai/odh-mlflow-rhel9 1791865967, rhoai/odh-autorag-rhel9 1791557539, rhoai/odh-trainer-rhel9 1791869783, +98 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
2 mo ago

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 9.4 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
CNA 3.1 9.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
CNA 4.0 9.4 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/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

Affected packages

ecosystem package affected fixed in
pypi nltk
<3.10.0
3.10.0

Affected products

  • nltk nltk

Classification

Weakness
  • CWE-502 Deserialization of Untrusted Data

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.