What is CVE-2019-11761?

CVE-2019-11761 is a medium-severity vulnerability in Mozilla Firefox, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 5.4/10. Published 2020-01-08.

How severe is CVE-2019-11761?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Is CVE-2019-11761 known to be exploited?

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

Auth bypass in Mozilla Firefox

CVE-2019-11761

By using a form with a data URI it was possible to gain access to the privileged JSONView object that had been cloned into content. Impact from exposing this object appears to be minimal, however it was a bypass of existing defense in depth mechanisms. This vulnerability affects Firefox < 70, Thunderbird < 68.2, and Firefox ESR < 68.2.

Vulnerability class: Race Condition

Published 2020-01-08 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.009 (58.6th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 58.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.009 · change: +0.001

Affected products

Mozilla Firefox — versions before 70
Mozilla Firefox Esr — versions before 68.2
Mozilla Firefox Esr
Mozilla Thunderbird — versions before 68.2
Canonical Ubuntu Linux — versions 16.04

Weakness classification (CWE)

Public proof-of-concept exploits

ARPSyndicate/cvemon

References

www.mozilla.org/security/advisories/mfsa2019-35/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2019-33/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2019-34/ (Vendor Advisory)
bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking)
security.gentoo.org/glsa/202003-10 (vendor-advisory, Third Party Advisory)
usn.ubuntu.com/4335-1/ (vendor-advisory, Third Party Advisory)

Frequently asked questions

What is CVE-2019-11761?: CVE-2019-11761 is a medium-severity vulnerability in Mozilla Firefox, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 5.4/10. Published 2020-01-08.
How severe is CVE-2019-11761?: Medium severity. CVSS v3 base score is 5.4 out of 10.
Is CVE-2019-11761 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.