What is CVE-2019-9789?

CVE-2019-9789 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2019-04-26.

How severe is CVE-2019-9789?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Mozilla Firefox

CVE-2019-9789

Mozilla developers and community members reported memory safety bugs present in Firefox 65. Some of these bugs showed evidence of memory corruption and we presume that with enough effort that some of these could be exploited to run arbitrary code. This vulnerability affects Firefox < 66.

Vulnerability class: Buffer Overflow

Published 2019-04-26 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.012 (68.4th percentile), scored 2026-10-25.

Low probability of exploitation in the next 30 days, but still tracked. 68th percentile — 68.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.012 · newest: 0.012 · change: 0.000

Affected products

Mozilla Firefox — versions unspecified

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

www.mozilla.org/security/advisories/mfsa2019-07/ (Vendor Advisory)
bugzilla.mozilla.org/buglist.cgi (Issue Tracking, Broken Link, Vendor Advisory)

Frequently asked questions

What is CVE-2019-9789?: CVE-2019-9789 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2019-04-26.
How severe is CVE-2019-9789?: Critical severity. CVSS v3 base score is 9.8 out of 10.