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Fencer Intel
critical 10.0

CVE-2026-0848 json

Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading

published 8mo ago modified 4mo ago also PYSEC-2026-99 , EUVD-2026-9875

cvss
10.0
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 58%
public exploits
0
none known

Summary

NLTK versions <=3.9.2 are vulnerable to arbitrary code execution due to improper input validation in the StanfordSegmenter module. The module dynamically loads external Java .jar files without verification or sandboxing. An attacker can supply or replace the JAR file, enabling the execution of arbitrary Java bytecode at import time. This vulnerability can be exploited through methods such as model poisoning, MITM attacks, or dependency poisoning, leading to remote code execution. The issue arises from the direct execution of the JAR file via subprocess with unvalidated classpath input, allowing malicious classes to execute when loaded by the JVM.

Patch / fix

  • pypi nltk 3.9.3
  • nltk Debian 14 3.9.3-1

debian advisories DEBIAN-CVE-2026-0848

  • nltk Ubuntu Pro 18.04 LTS 3.2.5-1ubuntu0.1+esm4
  • nltk Ubuntu Pro 20.04 LTS 3.4.5-2ubuntu0.1~esm4
  • nltk Ubuntu Pro 22.04 LTS 3.7-1ubuntu0.1~esm2
  • nltk Ubuntu Pro 24.04 LTS 3.8.1-1ubuntu0.1~esm2
  • nltk Ubuntu Pro 26.04 LTS 3.9.2-1ubuntu0.1~esm2

ubuntu advisories UBUNTU-CVE-2026-0848

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2026-0848 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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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-2026-0848 updated cvss 10.0

nltk: NLTK: Arbitrary code execution via unvalidated Java Archive (JAR) file loading

  • Red Hat Lightspeed Core lightspeed-core/lightspeed-stack-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-ocp-rag-rhel9, openshift-lightspeed/lightspeed-service-api-rhel9, openshift-lightspeed-tech-preview/lightspeed-rag-tool-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-ta-lmes-job-rhel9, rhoai/odh-llama-stack-core-rhel9, rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9, rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9
    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
yes
Technical impact
total
Assessed
8mo ago

Exploit prediction

0.84% chance of exploitation in the next 30 days, higher than 58% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • huntr.com https://huntr.com/bounties/08b109bb-ac24-403f-9422-1c246ce60202 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.0 10.0 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
OSV 3.0 10.0 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
pypi nltk
<3.9.3
3.9.3

Affected products

  • nltk nltk/nltk

Classification

Weakness
  • CWE-20 Improper Input Validation

References

Sources

Fencer Intel 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.