dovecot - Jan 2021 - CVE-2020-25275: MIME parsing crashes with particular messages

Open-Xchange Security Advisory 2021-01-04

Product: Dovecot
Vendor: OX Software GmbH
Internal reference: DOV-4113 (Bug ID)
Vulnerability type: CWE-20: Improper Input Validation
Vulnerable version: 2.3.11-2.3.11.3
Vulnerable component: lda, lmtp, imap
Report confidence: Confirmed
Solution status: Fixed by Vendor
Fixed version: 2.3.13
Vendor notification: 2020-09-10
Solution date: 2020-09-14
Public disclosure: 2021-01-04
CVE reference: CVE-2020-25275
CVSS: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L)
Researcher credit: Innokentii Sennovskiy (Rumata888) from BI.ZONE

Vulnerability Details:

Mail delivery / parsing crashed when the 10 000th MIME part was
message/rfc822 (or if parent was multipart/digest). This happened
due to earlier MIME parsing changes for CVE-2020-12100.

Risk:

Malicious sender can crash dovecot repeatedly by sending / uploading
message with more than 10 000 MIME parts.

Workaround:

These are usually dropped by MTA, where the mitigation can also be applied.

Solution:

Operators should update to 2.3.13 or later version.

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