[FD] CVE-2022-30550: Privilege escalation possible in dovecot when similar master and non-master passdbs are used

[Aki Tuomi via Fulldisclosure <fulldisclosure@xxxxxxxxxxxx>]

Affected product: Dovecot IMAP Server 
Internal reference: DOV-5320
Vulnerability type: Improper Access Control (CWE-284) 
Vulnerable version: 2.2
Vulnerable component: submission 
Report confidence: Confirmed 
Solution status: Fixed in main
Researcher credits: Julian Brook (julezman)
Vendor notification: 2022-05-06 
CVE reference: CVE-2022-30550
CVSS: 6.8 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N) 

Vulnerability Details: 
When two passdb configuration entries exist in Dovecot configuration, which 
have the same driver and args settings, the incorrect username_filter and 
mechanism settings can be applied to passdb definitions. These incorrectly 
applied settings can lead to an unintended security configuration and can 
permit privilege escalation with certain configurations involving master user 
authentication.

Dovecot documentation does not advise against the use of passdb definitions 
which have the same driver and args settings. One such configuration would be 
where an administrator wishes to use the same pam configuration or passwd file 
for both normal and master users but use the username_filter setting to 
restrict which of the users is able to be a master user.

Risk: 
If same passwd file or PAM is used for both normal and master users, it is 
possible for attacker to become master user.

Workaround:
Always authenticate master users from different source than regular users, e.g. 
using a separate passwd file. Alternatively, you can use global ACLs to ensure 
that only legimate master users have priviledged access.

Fix:
This has been fixed in main branch. See 
https://github.com/dovecot/core/compare/7bad6a24%5E..a1022072.patch
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