What is CVE-2019-9796?

CVE-2019-9796 is a critical-severity vulnerability in Mozilla Firefox, classified under Use After Free. CVSS score: 9.8/10. Published 2019-04-26.

How severe is CVE-2019-9796?

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

Is CVE-2019-9796 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Use After Free in Mozilla Firefox

CVE-2019-9796

A use-after-free vulnerability can occur when the SMIL animation controller incorrectly registers with the refresh driver twice when only a single registration is expected. When a registration is later freed with the removal of the animation controller element, the refresh driver incorrectly leaves a dangling pointer to the driver's observer array. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.

Vulnerability class: Use-After-Free

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: 0.021 (80.7th percentile), scored 2026-10-07.

Low probability of exploitation in the next 30 days, but still tracked. 81st percentile — 80.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.020 · newest: 0.021 · change: +0.000

Affected products

Mozilla Firefox — versions unspecified
Mozilla Firefox Esr — versions unspecified
Mozilla Thunderbird — versions unspecified

Weakness classification (CWE)

CWE-416 — Use After Free

Public proof-of-concept exploits

ARPSyndicate/cvemon

References

www.mozilla.org/security/advisories/mfsa2019-07/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2019-08/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2019-11/ (Vendor Advisory)
bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking, Vendor Advisory)
access.redhat.com/errata/RHSA-2019:0966 (vendor-advisory, Third Party Advisory)
access.redhat.com/errata/RHSA-2019:1144 (vendor-advisory, Third Party Advisory)

Frequently asked questions

What is CVE-2019-9796?: CVE-2019-9796 is a critical-severity vulnerability in Mozilla Firefox, classified under Use After Free. CVSS score: 9.8/10. Published 2019-04-26.
How severe is CVE-2019-9796?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2019-9796 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.