CVE-2020-28022: 
Exim vulnerability analysis and mitigation

Exim 4 before 4.94.2 contains a vulnerability identified as CVE-2020-28022, which involves an Improper Restriction of Write Operations within the Bounds of a Memory Buffer. This vulnerability specifically occurs when processing name=value pairs within MAIL FROM and RCPT TO commands. The issue was discovered and disclosed in May 2021, affecting all versions of Exim mail server before version 4.94.2 (NVD).

The vulnerability is classified as a heap out-of-bounds read and write vulnerability in the extract_option() function. It has been assigned a CVSS v3.1 Base Score of 9.8 (CRITICAL) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. The vulnerability is also associated with CWE-787 (Out-of-bounds Write) (NVD).

The vulnerability's critical CVSS score of 9.8 indicates severe potential impacts. The scoring suggests that successful exploitation could lead to complete compromise of system confidentiality, integrity, and availability. The attack vector being network-based (AV:N) with no required privileges (PR:N) or user interaction (UI:N) makes this vulnerability particularly dangerous (NVD).

The primary mitigation for this vulnerability is to upgrade Exim to version 4.94.2 or later. Various Linux distributions have released security updates to address this vulnerability. For example, Ubuntu has provided fixed versions for multiple releases including 4.94-15ubuntu1.2 for 22.04 LTS and 4.94-7ubuntu1.2 for 20.10 (Ubuntu Security).