CVE-2026-78207
Prototype pollution in exceljs-hardened allows Object.prototype modification via cell notes.
Is CVE-2026-78207 being exploited?
Not confirmed. CVE-2026-78207 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 0.44% probability of exploitation in the next 30 days.
How severe is CVE-2026-78207?
CVE-2026-78207 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-2026-78207?
Yes. A fix has been recorded for CVE-2026-78207. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-78207 affect?
CVE-2026-78207 affects exceljs-hardened < 5.0.0, Node.js applications using exceljs-hardened, Services parsing untrusted Excel cell notes. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-78207?
Upgrade to exceljs-hardened >=5.0.0 and validate/sanitize untrusted note JSON.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attackers can set __proto__ via parsed cell notes, modifying Object.prototype and causing data corruption, logic bypass, DoS or potential RCE in Node apps.
Patch when possible
- affected<= 4.4.0
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.