Affects widely-used Firefox/Thunderbird versions; high-risk browser vulnerability with CVSS 9.8.
CVE-2026-2775
Mitigation bypass in HTML Parser (DOM) across Firefox/Thunderbird
Is CVE-2026-2775 being exploited?
Not confirmed. CVE-2026-2775 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 0.55% probability of exploitation in the next 30 days.
How severe is CVE-2026-2775?
CVE-2026-2775 is rated Critical with a CVSS score of 9.8. 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-2026-2775?
Yes. A fix has been recorded for CVE-2026-2775. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-2775 affect?
CVE-2026-2775 affects Firefox < 148, Firefox ESR < 115.33, Firefox ESR < 140.8, Thunderbird < 148, 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-2026-2775?
Update to fixed versions as released; monitor advisories
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Mitigation bypass in HTML parser could enable exploitation on affected browsers, potentially bypassing security checks and enabling code execution.
Patch when possible