Mozilla Firefox encounters zero-day vulnerability in targeted attacks

Mozilla Foundation has released a security advisory to address a critical zero-day flaw in Mozilla Firefox, which has been exploited in targeted attacks.

CVE-2019-17026 is a type confusion vulnerability in IonMonkey, the JavaScript Just-In-Time (JIT) compiler for SpiderMonkey, Mozilla's JavaScript engine. According to Mozilla's advisory, the flaw exists in the JIT compiler due to "incorrect alias information for setting array elements," specifically in StoreElementHole and FallibleStoreElement.

The vulnerability was reported to Mozilla by researchers at Qihoo 360 ATA. Mozilla's advisory states they are "aware of targeted attacks in the wild abusing this flaw." Based on this note in the advisory, it appears the vulnerability was exploited in the wild as a zero-day.

This advisory follows the release of Firefox 72 and Firefox Extended Support Release (ESR) 68.4 on January 7, which included the following security advisories -

* Firefox 72: Mozilla Foundation Security Advisory 2020-01

* Firefox ESR 68.4: Mozilla Foundation Security Advisory 2020-02

Last year, Mozilla patched CVE-2019-11707, another type confusion flaw that was used in conjunction with CVE-2019-11708, a sandbox escape vulnerability in targeted attacks. At this time, no proof of concept is available for this vulnerability. To address CVE-2019-17026, Mozilla released Firefox 72.0.1 and Firefox ESR 68.4.1. Because this vulnerability has been exploited in targeted attacks, Firefox users are advised to upgrade as soon as possible.

Satnam Narang
Senior Security Response Manager at Tenable