Affects widely-used Mozilla Firefox/Thunderbird; critical same-origin bypass enabling cross-origin data leakage.
CVE-2026-2790
Same-origin policy bypass in Networking: JAR; affects Firefox/Thunderbird <148/ESR <140.8.
Is CVE-2026-2790 being exploited?
Not confirmed. CVE-2026-2790 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 0.23% probability of exploitation in the next 30 days.
How severe is CVE-2026-2790?
CVE-2026-2790 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-2026-2790?
Yes. A fix has been recorded for CVE-2026-2790. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-2790 affect?
CVE-2026-2790 affects Mozilla Firefox < 148, Firefox ESR < 140.8, Mozilla Thunderbird < 148, Thunderbird < 140.8. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-2790?
Upgrade to latest Firefox/Thunderbird; enable auto-update
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Cross-origin bypass allows a malicious page to read data from other origins via the browser.
Patch when possible