NLTK up to 3.10.2 AllowlistUnpickler TransitionParser.parse code injection

Summaryinfo

A vulnerability was found in NLTK up to 3.10.2. It has been classified as critical. Affected by this issue is the function TransitionParser.parse of the component AllowlistUnpickler. Performing a manipulation results in code injection. This vulnerability is cataloged as CVE-2026-71513. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as critical, was found in NLTK up to 3.10.2. This affects the function TransitionParser.parse of the component AllowlistUnpickler. The manipulation with an unknown input leads to a code injection vulnerability. CWE is classifying the issue as CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

NLTK before 3.10.3 contains a remote code execution vulnerability in AllowlistUnpickler that validates only the pickle module string and not the global name, allowing attackers to resolve dotted names by attribute traversal to callables outside the allowlisted namespace. Attackers can craft untrusted transition-parser models that execute arbitrary commands when TransitionParser.parse loads the model through allowlisted_pickle_load.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-71513 since 08/06/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059 for this issue.

Upgrading to version 3.10.3 eliminates this vulnerability.

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Productinfo

Name

• NLTK

Version

• 3.10.0
• 3.10.1
• 3.10.2

Website

• Product: https://github.com/nltk/nltk/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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