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Advisory details: pypa / nltk/PYSEC-2026-99
Advisory ID pypa/nltk/PYSEC-2026-99
Aliases CVE-2026-0848
PYSEC-2026-99
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.
Status Published
Exploitability 0.5
Weighted Severity 9.0
Risk 4.5
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (0)
There are no known CWE.
System Score Found at
cvssv3 10.0 https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-99.yaml
Reference id Reference type URL
08b109bb-ac24-403f-9422-1c246ce60202 Other https://huntr.com/bounties/08b109bb-ac24-403f-9422-1c246ce60202
No exploits are available.

No EPSS data available for this advisory.

Patch URL
There are no known patches.
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H Found at https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-99.yaml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none

Vector: SSVCv2/E:P/A:Y/T:T/P:M/B:A/M:M/D:R/2026-03-06T16:30:57Z/

Decision: Track*

Source URL: https://github.com/cisagov/vulnrichment/blob/develop/2026/0xxx/CVE-2026-0848.json

Source Advisory: vulnrichment/CVE-2026-0848

View SSVC decision tree 
[{'Exploitation': 'poc'},
 {'Automatable': 'yes'},
 {'Technical Impact': 'total'},
 {'Mission Prevalence': 'minimal'},
 {'Public Well-being Impact': 'material'},
 {'Mission & Well-being': 'medium'}]