CVE-2020-9856: 
macOS vulnerability analysis and mitigation

CVE-2020-9856 is a security vulnerability affecting macOS Catalina versions prior to 10.15.5. The vulnerability was discovered by researchers @jinmo123, @setuid0x0_, and @insu_yun_en of @SSLab_Gatech working with Trend Micro's Zero Day Initiative and was patched by Apple in May 2020 (Apple Advisory). The vulnerability exists in the CVMS (Core Virtual Memory System) component of macOS and could allow an application to gain elevated privileges on the system.

The vulnerability is related to improper checks in the CVMS component of macOS. When exploited, it allows an application to gain elevated privileges through a heap overflow in the CVM server. The vulnerability has a CVSS v3.1 base score of 5.3 (Medium) with the vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L, indicating that it requires local access and low privileges to exploit (NVD).

If successfully exploited, this vulnerability allows a malicious application to gain elevated privileges on the affected system. This could potentially lead to unauthorized access to system resources and compromise of system security (Apple Advisory).

The vulnerability has been demonstrated to be exploitable in real-world conditions. It was notably used as part of a chain exploit in Safari at Pwn2Own 2020, where it was combined with other vulnerabilities to achieve sandbox escape and privilege escalation. The exploit chain involved using CVE-2020-9856 to extract a macOS application containing a payload into /var/db/CVMS and subsequently executing it (Rapid7).

Apple has addressed this vulnerability with improved checks in macOS Catalina 10.15.5. Users should update their systems to this version or later to protect against this vulnerability. The fix is included in the Security Update 2020-003 for macOS Catalina (Apple Advisory).