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Mozilla Patches Firefox Zero-Day Exploited in Targeted Attacks

Updates released by Mozilla on Wednesday for its Firefox browser address a zero-day vulnerability that has been exploited in targeted attacks.

The vulnerability, tracked as CVE-2019-17026 and classified as having critical impact, has been described by Mozilla as an “IonMonkey type confusion with StoreElementHole and FallibleStoreElement.” IonMonkey is the Just-in-Time (JIT) compiler for Firefox’s SpiderMonkey JavaScript engine.

“Incorrect alias information in IonMonkey JIT compiler for setting array elements could lead to a type confusion,” Mozilla explained in its advisory.

Mozilla says it’s aware of targeted attacks exploiting this zero-day, but no other information has been made available.

A Current Activity bulletin released by the U.S. Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency (CISA) says the vulnerability could allow an attacker to take control of an affected system.

The flaw has been patched with the release of Firefox 72.0.1 and Firefox ESR 68.4.1, and users have been advised to update their installations.

Mozilla has credited Chinese cybersecurity company Qihoo 360 for informing it about the vulnerability. ZDNet reported that Qihoo 360 posted a tweet saying that the Firefox zero-day had been exploited alongside an Internet Explorer zero-day, but the tweet has been deleted and there is no word from Microsoft regarding an Internet Explorer zero-day.

Mozilla last year patched two Firefox zero-day vulnerabilities that had been exploited to deliver Mac malware to cryptocurrency exchanges.

The organization this week released Firefox 72, which improves privacy by allowing users to delete telemetry data and by blocking fingerprinting scripts by default. Firefox 72 also patches nearly a dozen vulnerabilities, including 5 rated high severity. 

Related: Tech Support Scammers Exploiting Unpatched Firefox Bug

Related: Mac Malware Delivered via Firefox Exploits Analyzed

Related: Firefox Zero-Day Exploited to Deliver Malware to Cryptocurrency Exchanges

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.