CVE-2020-28016: 
Exim vulnerability analysis and mitigation

CVE-2020-28016 affects Exim 4 before version 4.94.2. The vulnerability is an off-by-two Out-of-bounds Write that occurs when '-F ''' is mishandled by parse_fix_phrase(). This vulnerability was introduced in Exim 4.94 through a code change intended to fix a taint trap in parse_fix_phrase() (Exim Advisory).

The vulnerability occurs in parse_fix_phrase() function when processing an empty originator_name (-F ''). The function allocates a zero-sized buffer but attempts to write a null byte to buffer[1], resulting in an out-of-bounds write. The CVSS v3.1 base score is 7.8 HIGH (Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) (NVD).

The vulnerability could potentially allow an unprivileged local attacker to obtain full root privileges if successfully exploited. The vulnerability affects the system's confidentiality, integrity, and availability with high severity ratings (NVD).

The vulnerability requires local access and low privileges to exploit. While no public exploits are confirmed, the vulnerability is considered relatively straightforward to exploit due to its nature as a buffer overflow issue (Exim Advisory).

The vulnerability was fixed in Exim version 4.94.2. Users should upgrade to this version or later to mitigate the risk. The fix addresses the buffer allocation and write issue in the parse_fix_phrase() function (Debian Tracker).