CVE-2020-4033: 
NixOS vulnerability analysis and mitigation

In FreeRDP before version 2.1.2, there is an out of bounds read vulnerability in RLEDECOMPRESS. This vulnerability, identified as CVE-2020-4033, affects all FreeRDP based clients with sessions using color depth less than 32 bits. The vulnerability was discovered and disclosed in June 2020, and was fixed in FreeRDP version 2.1.2 (GitHub Advisory).

The vulnerability is classified with a CVSS 3.1 score of 6.5 (Medium severity), with the following characteristics: Network attack vector, Low attack complexity, No privileges required, No user interaction needed, Unchanged scope, Low confidentiality impact, No integrity impact, and Low availability impact. The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L (Ubuntu Security).

The vulnerability could lead to an out of bounds read of up to 4 bytes when processing RDP sessions with color depth less than 32 bits. This could potentially result in information disclosure or denial of service conditions (GitHub Advisory).

The vulnerability has a low attack complexity and requires no special privileges or user interaction to exploit. However, there are no known public exploits specifically targeting this vulnerability in the wild (GitHub Advisory).

The primary mitigation is to upgrade to FreeRDP version 2.1.2 or later, which contains the fix for this vulnerability. As a workaround, users can connect using /bpp:32 to force 32-bit color depth, which avoids the vulnerable code path (GitHub Advisory, FreeRDP Release).