How severe is CVE-2026-78683?

CVE-2026-78683 has a CVSS 3.x base score of 9.6, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-78683 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-78683?

CVE-2026-78683 affects Nltk. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-78683?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2026-78683 published?

CVE-2026-78683 was published on 2026-08-25 and last updated on 2026-08-31.

CVE-2026-78683

CVE-2026-78683 is a critical-severity vulnerability in Nltk with a CVSS 3.x base score of 9.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-502.

Key facts

Severity: Critical (CVSS 3.x base score 9.6)
CVSS v4: 9.4
EPSS exploit prediction: 1% (42nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-502
Affected product: Nltk
Published: 2026-08-25
Last modified: 2026-08-31

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.

Frequently asked questions

What is CVE-2026-78683?: 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.
How severe is CVE-2026-78683?: CVE-2026-78683 has a CVSS 3.x base score of 9.6, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-78683 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-78683?: CVE-2026-78683 affects Nltk. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-78683?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2026-78683 published?: CVE-2026-78683 was published on 2026-08-25 and last updated on 2026-08-31.

References

Affected products (1)

cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*

More vulnerabilities in Nltk

CVE-2026-0848 — Critical (CVSS 10.0): NLTK versions <=3.9.2 are vulnerable to arbitrary code execution due to improper input validation in the…
CVE-2026-79675 — Critical (CVSS 9.8): NLTK before 3.10.3 fails to validate JVM options passed through the per-call options parameter in the java() function,…
CVE-2026-79657 — Critical (CVSS 9.8): NLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that trust…
CVE-2026-71513 — High (CVSS 8.8): NLTK before 3.10.3 contains a remote code execution vulnerability in AllowlistUnpickler that validates only the pickle…
CVE-2025-14009 — High (CVSS 8.8): A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The _unzip_iter…
CVE-2026-79674 — High (CVSS 8.2): NLTK versions before 3.10.3 contain a path sandbox bypass vulnerability in corpus-reader constructors that allows…

All CVEs affecting Nltk →

Other CWE-502 (Deserialization of Untrusted Data) vulnerabilities

CVE-2026-70416 — Critical (CVSS 10.0): Dell ObjectScale, versions prior to 4.4.0.0, contains a Deserialization of Untrusted Data vulnerability. An…
CVE-2026-82222 — Critical (CVSS 10.0): Deserialization of Untrusted Data vulnerability in Liquid Web / StellarWP GiveWP allows Object Injection. This issue…
CVE-2026-69836 — Critical (CVSS 10.0): Deserialization of untrusted data in Microsoft Entra ID allows an unauthorized attacker to execute code over a network.
CVE-2026-17061 — Critical (CVSS 10.0): A Deserialization of Untrusted Data vulnerability affecting SIMULIA Execution Engine from Release 2023 through Release…
CVE-2026-11756 — Critical (CVSS 10.0): A Deserialization of Untrusted Data vulnerability affecting Station Launcher App in 3DEXPERIENCE platform from Release…
CVE-2026-41104 — Critical (CVSS 10.0): Deserialization of untrusted data in Microsoft Planetary Computer Pro allows an unauthorized attacker to disclose…

Browse all CWE-502 (Deserialization of Untrusted Data) vulnerabilities →