CVE-2020-15469: 
NixOS vulnerability analysis and mitigation

In QEMU 4.2.0, a vulnerability was discovered where a MemoryRegionOps object may lack read/write callback methods, leading to a NULL pointer dereference. The vulnerability was assigned CVE-2020-15469 and was reported by Lei Sun. The issue was first disclosed on July 2, 2020, affecting QEMU system emulators (Openwall, MITRE).

The vulnerability occurs during Memory-Mapped I/O (MMIO) read/write operations when the respective handler function is not defined. This results in a NULL pointer dereference in various system emulators of QEMU. The issue has a CVSS 3.1 Base Score of 2.3 (Low) with the following vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L (Ubuntu).

The vulnerability's impact is limited to a denial of service (DoS) condition. A privileged guest user can only use this issue to perform a denial of service to their own instance by crashing the QEMU process on the host (Openwall).

The vulnerability requires local access and high privileges to exploit. A privileged guest user must be able to invoke MMIO operations to trigger the vulnerability. There are no known reports of this vulnerability being exploited in the wild (Ubuntu).

The vulnerability has been fixed in multiple versions across different distributions. For Ubuntu, fixes were implemented in versions ranging from 1:2.11+dfsg-1ubuntu7.37 for 18.04 LTS to 1:6.0+dfsg-1~ubuntu3 for newer releases. Debian addressed the issue in version 1:2.8+dfsg-6+deb9u13 for Debian 9 stretch and 1:3.1+dfsg-8+deb10u9 for Debian 10 buster (Debian LTS, Ubuntu).