Gptline: NLTK AllowlistUnpickler dotted-name validation bypass allows remote code execution (CVE-2026-71513)
Description
NLTK versions before 3.10.3 contain a remote code execution vulnerability in the AllowlistUnpickler component. The vulnerability arises because the validation only checks the pickle module string but not the full global name, allowing attackers to exploit attribute traversal to invoke callables outside the intended allowlist. This can be triggered by crafting malicious transition-parser models that execute arbitrary commands when loaded via TransitionParser.parse.
CVSS v3.1
Score 8.8high
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability (CVE-2026-71513) affects NLTK before version 3.10.3, specifically in the AllowlistUnpickler class. It improperly validates only the pickle module string and not the full dotted global name, enabling attackers to bypass the allowlist by resolving dotted names through attribute traversal. This flaw allows remote code execution when untrusted transition-parser models are loaded using allowlisted_pickle_load in TransitionParser.parse. The CVSS 3.1 score is 8.8, indicating high severity with network attack vector, low attack complexity, no privileges required, and user interaction needed.
Potential Impact
Successful exploitation allows remote attackers to execute arbitrary code on the affected system by supplying malicious transition-parser models. This can lead to full compromise of the environment running the vulnerable NLTK version.
Mitigation Recommendations
A patch is available for this vulnerability. Users should upgrade NLTK to version 3.10.3 or later. No additional mitigations are specified in the advisory.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-5gh2-94qg-qppq
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-71513"]
- Database Specific Severity
- HIGH
- Cvss Version
- 3.1
Threat ID: 6a8a27f9acd9273b499bc9d0
Added to database: 08/22/2026, 22:51:37 UTC
Last enriched: 09/18/2026, 02:17:18 UTC
Last updated: 10/06/2026, 18:48:24 UTC
Views: 109
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