Vulnerability · Published Aug 22, 2026 · Assigned by VulnCheck

CVE-2026-71513NLTK 3.10.0 through 3.10.2 Remote Code Execution via AllowlistUnpickler Dotted-Name Bypass

High 8.8

In plain English

A high-severity unsafe deserialization in nltk from nltk. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.1% (higher than 66% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.8High

Exploit odds (30 days)1.1%top 34.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	nltk	no fix listed	DEBIAN-CVE-2026-71513
Debian:13	nltk	no fix listed	DEBIAN-CVE-2026-71513
Debian:14	nltk	3.10.3-1	DEBIAN-CVE-2026-71513
PyPI	nltk	3.10.3	GHSA-5gh2-94qg-qppq
PyPI	nltk	3.10.3	PYSEC-2026-3867
Ubuntu:26.10	nltk	no fix listed	UBUNTU-CVE-2026-71513

Affected products (as reported)

Vendor	Product	Versions
nltk	nltk	3.10.0 – before 3.10.3

Weakness: CWE-502 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

References

Patch Commit patch
https://github.com/nltk/nltk product
https://github.com/nltk/nltk/blob/v3.10.2/nltk/picklesec.py#L119-L124 technical-description
VulnCheck Advisory: NLTK 3.10.0 through 3.10.2 Remote Code Execution via AllowlistUnpickler Dotted-Name Bypass third-party-advisory