CVE-2026-63310
NLTK downloader allows unverified package extraction enabling remote code execution via MITM.
Is CVE-2026-63310 being exploited?
Not confirmed. CVE-2026-63310 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 0.12% probability of exploitation in the next 30 days.
How severe is CVE-2026-63310?
CVE-2026-63310 is rated Critical with a CVSS score of 9.3. 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-2026-63310?
Yes. A fix has been recorded for CVE-2026-63310. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-63310 affect?
CVE-2026-63310 affects NLTK < 3.9.3, Python apps using nltk.downloader, Developer workstations, CI/CD pipelines fetching NLTK data, and 1 further product or version. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-63310?
Upgrade NLTK to >=3.9.3, block runtime downloads, and validate packages
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote arbitrary code execution and supply-chain compromise via unverified NLTK downloader (MITM/DNS poisoning) leading to malicious package extraction.
Immediate action required
- affected< 3.9.3
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.