Mozilla patched two Firefox browser zero-day vulnerabilities actively being exploited in the wild. The flaws, both use-after-free bugs, have been part of “targeted attacks in the wild,” according to a Mozilla Foundation security advisory posted Friday.
Both bugs have critical ratings and allow remote attackers to execute arbitrary code or trigger crashes on machines running versions of Firefox prior to 74.0.1 and its business-friendly Firefox Extended Support Release 68.6.1. The bugs impact Firefox browser versions running on Windows, macOS and Linux operating systems. Details are scant on how either bug (CVE-2020-6819 and CVE-2020-6820) are specifically being exploited by adversaries.
Tracked as CVE-2020-6819, this bug is a use-after free vulnerability tied to the browser component “nsDocShell destructor”. The Firefox nsDocShell is a client of the nsI-HttpChannel API, a function of the browser related to reading HTTP headers.
The second vulnerability, tracked as CVE-2020-6820, is also a use-after-free bug actively being exploited in the wild. In this case, the attackers are targeting the Firefox browser component ReadableStream, an interface of the Streams API. The Streams API is “responsible for breaking a resource that you want to receive over a network down into small chunks,” according to Mozilla.
Bugs were reported by security researchers Francisco Alonso and Javier Marcos of JMP Security.
“There is still lots of work to do and more details to be published (including other browsers). Stay tuned,” tweeted Alonso.
There is still lots of work to do and more details to be published (including other browsers). Stay tuned.
— Francisco Alonso (@revskills) April 3, 2020
“Successful exploitation of the most severe of these vulnerabilities could allow for arbitrary code execution,” according to a Center for Internet Security bulletin. “Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than those who operate with administrative user rights.”
Patches are available for multiple version of the Firefox browser including: Firefox 74.0.1 for Windows 64-bit, Firefox 74.0.1 for Windows 32-bit, Firefox 74.0.1 for macOS, Firefox 74.0.1 for Linux 64-bit and Firefox 74.0.1 for Linux 32-bit.