CVE-2026-78683
Unsafe pickle deserialization in NLTK TransitionParser allows arbitrary code execution when loading models
Is CVE-2026-78683 being exploited?
Not confirmed. CVE-2026-78683 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.29% probability of exploitation in the next 30 days.
How severe is CVE-2026-78683?
CVE-2026-78683 is rated Critical with a CVSS score of 9.4. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-78683?
Yes. A fix has been recorded for CVE-2026-78683. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-78683 affect?
CVE-2026-78683 affects NLTK <= 3.9.4, nltk.parse.transitionparser.TransitionParser.parse(), Python apps loading NLTK model files. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-78683?
Upgrade to NLTK >=3.10.0; avoid loading untrusted models; use RestrictedUnpickler or sandboxing
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Arbitrary code execution as the application user via loading attacker-crafted NLTK model files (pickle gadget chains).
Immediate action required
- affected< 3.10.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.