CVE-2023-51764

Published: 24 December 2023

Postfix through 3.8.5 allows SMTP smuggling unless configured with smtpd_data_restrictions=reject_unauth_pipelining and smtpd_discard_ehlo_keywords=chunking (or certain other options that exist in recent versions). Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Postfix supports <LF>.<CR><LF> but some other popular e-mail servers do not. To prevent attack variants (by always disallowing <LF> without <CR>), a different solution is required, such as the smtpd_forbid_bare_newline=yes option with a Postfix minimum version of 3.5.23, 3.6.13, 3.7.9, 3.8.4, or 3.9.

Notes

Author	Note
mdeslaur	We will not be releasing updates for Lunar which is EoL on 2024-01-25

Mitigation

Patched versions of Postfix before 3.9 require the below configs for the
fix to apply:
smtpd_forbid_bare_newline = normalize
smtpd_forbid_bare_newline_exclusions = $mynetworks

Priority

Cvss 3 Severity Score

5.3

Score breakdown

Status

Package	Release	Status
postfix Launchpad, Ubuntu, Debian	bionic	Released (3.3.0-1ubuntu0.4+esm3) Available with Ubuntu Pro or Ubuntu Pro (Infra-only)
	focal	Released (3.4.13-0ubuntu1.4)
	jammy	Released (3.6.4-1ubuntu1.3)
	lunar	Ignored (end of life)
	mantic	Released (3.8.1-2ubuntu0.2)
	trusty	Released (2.11.0-1ubuntu1.2+esm3) Available with Ubuntu Pro or Ubuntu Pro (Infra-only)
	upstream	Released (3.8.4-1)
	xenial	Released (3.1.0-3ubuntu0.4+esm3) Available with Ubuntu Pro or Ubuntu Pro (Infra-only)

Severity score breakdown

Parameter	Value
Base score	5.3
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	Low
Availability impact	None
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

References

Bugs

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