This vulnerability was reported to iDefense by anonymous. NSS was ready to pay for exploit for this vulnerability $100-500.
The vulnerability was used to compromise Philippines human rights website.
Advisory: SB2011041201 - Multiple vulnerabilities in Microsoft Internet Explorer
Vulnerable component: Microsoft Internet Explorer
CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H/E:H/RL:O/RC:C
CWE-ID: CWE-416 - Use After Free
The vulnerability allows a remote attacker to execute arbitrary code on the target system.
The weakness exists due to use-after-free error when handling layout objects that have not been correctly initialized or have been deleted. A remote attacker can create a specially crafted Web site, trick the victim into visiting it, trigger memory corruption and execute arbitrary code on the system with privileges of the current user.
Successful exploitation of the vulnerability results in arbitrary code execution on the vulnerable system.
Note: the vulnerability was being actively exploited.