Microsoft this week patched several memory corruption vulnerabilities in the Edge web browser that were disclosed at the 2017 Pwn2Own hacking competition.

The white hat hackers who signed up for this year’s Pwn2Own earned a total of more than $800,000 for vulnerabilities in Windows, macOS, Ubuntu, Safari, Firefox, Edge, Flash Player, Adobe Reader, and VMware Workstation.

VMware, Mozilla, Adobe, Apple and Linux kernel developers addressed the flaws affecting their products in March and April, and Microsoft has now also started releasing patches. The Zero Day Initiative (ZDI), which organizes Pwn2Own, published six advisories on Wednesday for each of the security holes fixed by Microsoft.

The vulnerabilities affect the scripting engines used by Edge, including the Chakra JavaScript engine, and they can lead to privilege escalation, information disclosure and remote code execution. The following CVE identifiers have been assigned: CVE-2017-0233, CVE-2017-0234, CVE-2017-0240, CVE-2017-0238 and CVE-2017-0228.

According to ZDI, the use-after-free and heap-based buffer overflow vulnerabilities are related to the handling of Array, AudioBuffer, Array.unshift and ArrayBuffer objects. An attacker can exploit the flaws by getting the targeted user to visit a malicious website or open a specially crafted file.

Each of the vulnerabilities patched this week by Microsoft has a severity rating of “medium” in the ZDI advisories, with CVSS scores ranging from 4.3 to 6.9. Microsoft has assigned “critical” severity ratings to only two of the flaws: CVE-2017-0228 and CVE-2017-0240.

While not particularly dangerous on their own, some of the weaknesses can be highly valuable for attackers when combined with other bugs, as researchers demonstrated at the Pwn2Own competition.

There is no evidence that any of these flaws have been exploited in the wild, and exploits have not been released by the experts who found them.

Pwn2Own participants also disclosed several Windows vulnerabilities, including ones leveraged in exploit chains targeting Adobe products and web browsers, but it’s unclear if the Windows flaws have been patched as well.

Microsoft released patches for more than 50 vulnerabilities this week, including four zero-days that have been exploited in attacks by profit-driven cybercriminals and cyber espionage groups linked to Russia.

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