CVE-2026-78681
XML entity expansion DoS in NLTK before 3.10.3
Is CVE-2026-78681 being exploited?
Not confirmed. CVE-2026-78681 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-2026-78681?
CVE-2026-78681 is rated High with a CVSS score of 8.7. 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-2026-78681?
Yes. A fix has been recorded for CVE-2026-78681. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-78681 affect?
CVE-2026-78681 affects NLTK < 3.10.3, Python applications using NLTK XML parsing modules. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-78681?
Upgrade NLTK to >=3.10.3; avoid parsing untrusted XML or use secure XML parsers (e.g., defusedxml).
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote Denial of Service: crafted XML with nested entity declarations causes memory/CPU exhaustion during NLTK XML parsing, crashing or hanging services.
Immediate action required
- affected< 3.10.3
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.