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CVE-2026-78683

Nltk insecure deserialization

9.6 CRITICALPublic exploitEPSS 0.51%
  1. Published25 Aug 2026

Description

NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionRequired
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Affected products

Nltk< 3.10.0

Remediation

Fixed in
Nltk≥ 3.10.0

References

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Frequently asked

Is CVE-2026-78683 being actively exploited?

CVE-2026-78683 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.51%.

How severe is CVE-2026-78683?

CVE-2026-78683 has a CVSS 3.1 base score of 9.6, rated critical. EPSS estimates a 0.51% probability of exploitation.

Which products are affected by CVE-2026-78683?

Affected products include Nltk.

How do I fix CVE-2026-78683?

Upgrade affected software to a fixed version, for example Nltk 3.10.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-78683 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.