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/trans…
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | nltk | <= 3.9.4 | 3.10.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Nltk | Nltk | before 3.10.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-rhp5-r9x4-f5g2
- https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2
- https://nvd.nist.gov/vuln/detail/CVE-2026-78683
- https://github.com/nltk/nltk/pull/3631
- https://github.com/nltk/nltk/commit/f26b3753038d937b68145daf15e9636f8451053c
- https://github.com/nltk/nltk/releases/tag/v3.10.0
- https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3734.yaml
- https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization