CVE-2020-7957: 
Dovecot vulnerability analysis and mitigation

The vulnerability CVE-2020-7957 affects the IMAP and LMTP components in Dovecot 2.3.9 before version 2.3.9.3. The vulnerability was discovered on January 14, 2020, and publicly disclosed on February 12, 2020. The issue involves mishandling of snippet generation when many characters must be read to compute the snippet and a trailing '>' character exists (Openwall Advisory, NVD).

The vulnerability occurs in snippet generation under specific conditions: when the message is large enough that message-parser returns multiple body blocks, the first block(s) don't contain the full snippet (e.g., full of whitespace), and the input ends with a '>' character. The vulnerability has been assigned a CVSS score of 3.1 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L), indicating a low severity with network attack vector requiring high attack complexity (Openwall Advisory).

When exploited, this vulnerability can cause a denial of service condition where the recipient cannot read all of their messages. Specifically, sending specially crafted email can cause mailbox to have permanently inaccessible mail, or the mail can be stuck in delivery (Openwall Advisory).

The vulnerability was fixed in Dovecot version 2.3.9.3. Users are advised to upgrade to this version or later to mitigate the issue. The fix was released as part of security updates for various distributions, including Fedora 30 and 31 (Fedora Update).