The IonMonkey just-in-time (JIT) compiler can leak an internal JS_OPTIMIZED_OUT magic value to the running script during a bailout. This magic value can then be used by JavaScript to achieve memory corruption, which results in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.
https://www.mozilla.org/security/advisories/mfsa2019-11/
https://www.mozilla.org/security/advisories/mfsa2019-08/
https://www.mozilla.org/security/advisories/mfsa2019-07/
https://bugzilla.mozilla.org/show_bug.cgi?id=1532599
https://access.redhat.com/errata/RHSA-2019:0966
https://access.redhat.com/errata/RHSA-2019:1144
http://packetstormsecurity.com/files/153106/Spidermonkey-IonMonkey-JS_OPTIMIZED_OUT-Value-Leak.html
Source: MITRE
Published: 2019-04-26
Updated: 2022-03-30
Type: CWE-787
Base Score: 7.5
Vector: AV:N/AC:L/Au:N/C:P/I:P/A:P
Impact Score: 6.4
Exploitability Score: 10
Severity: HIGH
Base Score: 9.8
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Impact Score: 5.9
Exploitability Score: 3.9
Severity: CRITICAL