CVE-2026-0877
Mitigation bypass in Firefox DOM; affects Firefox <147 and ESR <115.32/140.7.
Is CVE-2026-0877 being exploited?
Not confirmed. CVE-2026-0877 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 0.48% probability of exploitation in the next 30 days.
How severe is CVE-2026-0877?
CVE-2026-0877 is rated High with a CVSS score of 8.1. 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-2026-0877?
Yes. A fix has been recorded for CVE-2026-0877. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-0877 affect?
CVE-2026-0877 affects Mozilla Firefox < 147, Firefox ESR < 115.32, Firefox ESR < 140.7. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-0877?
Update Firefox to latest release (147+ or ESR patched).
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypasses Firefox DOM security mitigations, enabling attacker-controlled actions in the browser.
Patch when possible