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Advisory details: pypa / nltk/PYSEC-2026-3867
Advisory ID pypa/nltk/PYSEC-2026-3867
Aliases CVE-2026-71513
GHSA-5gh2-94qg-qppq
PYSEC-2026-3867
Summary NLTK AllowlistUnpickler dotted-name validation bypass allows remote code execution 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.
Status Published
Exploitability 0.5
Weighted Severity 7.9
Risk 4.0
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
cvssv3.1 8.8 https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-3867.yaml
cvssv4 8.7 https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-3867.yaml
Reference id Reference type URL
https://github.com/advisories/GHSA-5gh2-94qg-qppq
https://github.com/nltk/nltk
https://github.com/nltk/nltk/blob/v3.10.2/nltk/picklesec.py#L119-L124
https://github.com/nltk/nltk/commit/c3e37113742a1ebeeb4f2ca58941f320f98805ea
https://pypi.org/project/nltk
https://www.vulncheck.com/advisories/nltk-through-remote-code-execution-via-allowlistunpickler-dotted-name-bypass
CVE-2026-71513 https://nvd.nist.gov/vuln/detail/CVE-2026-71513
No exploits are available.

No EPSS data available for this advisory.

Patch URL
There are no known patches.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Found at https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-3867.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: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N Found at https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-3867.yaml
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

high

none

passive

active

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

There are no SSVC decisions available.