CVE-2023-51764

postfix: SMTP smuggling vulnerability

Severity Score

5.3

*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

*Multiple Sources

Exploited in Wild

*KEV

Decision

*SSVC

Descriptions

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.

Postfix hasta 3.8.4 permite el contrabando SMTP a menos que se configure con smtpd_data_restrictions=reject_unauth_pipelining (u otras opciones que existen en versiones recientes). Los atacantes remotos pueden utilizar una técnica de explotación publicada para inyectar mensajes de correo electrónico que parecen originarse en el servidor Postfix, lo que permite omitir un mecanismo de protección SPF. Esto ocurre porque Postfix admite . pero algunos otros servidores de correo electrónico populares no lo hacen. Para evitar variantes de ataque (al no permitir siempre sin ), se requiere una solución diferente: la opción smtpd_forbid_bare_newline=yes con una versión mínima de Postfix de 3.5.23, 3.6.13, 3.7.9, 3.8.4, o 3.9.

A flaw was found in some SMTP server configurations in Postfix. This flaw allows a remote attacker to break out email message data to "smuggle" SMTP commands and send spoofed emails that pass SPF checks.

Out of the box, Postfix targets to accommodate older clients with faulty SMTP implementations due to which restrictions are not enforced in the default configuration. Appropriate mitigation strategies are mentioned in the appropriate section below.

*Credits: N/A

CVSS Scores

NISTv3.1 5.3

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

* Common Vulnerability Scoring System

SSVC

Decision:-

Exploitation

Automatable

Tech. Impact

* Organization's Worst-case Scenario

Timeline

2023-12-24 CVE Reserved
2023-12-24 CVE Published
2024-01-03 First Exploit
2024-08-02 CVE Updated
2024-09-13 EPSS Updated
---------- Exploited in Wild
---------- KEV Due Date

CWE

CWE-345: Insufficient Verification of Data Authenticity
CWE-451: User Interface (UI) Misrepresentation of Critical Information

CAPEC

References (19)

URL	Tag	Source
http://www.openwall.com/lists/oss-security/2023/12/24/1	Mailing List
http://www.openwall.com/lists/oss-security/2023/12/25/1	Mailing List
http://www.openwall.com/lists/oss-security/2024/05/09/3	Mailing List
https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html	Technical Description
https://lists.debian.org/debian-lts-announce/2024/01/msg00020.html	Mailing List
https://lwn.net/Articles/956533
https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide	Technical Description
https://www.openwall.com/lists/oss-security/2024/01/22/1
https://www.postfix.org/announcements/postfix-3.8.5.html

URL	Date	SRC
https://github.com/duy-31/CVE-2023-51764	2024-08-02
https://github.com/eeenvik1/CVE-2023-51764	2024-08-02
https://github.com/Double-q1015/CVE-2023-51764	2024-01-05
https://github.com/d4op/CVE-2023-51764-POC	2024-01-03
https://www.postfix.org/smtp-smuggling.html	2024-08-02
https://www.youtube.com/watch?v=V8KPV96g1To	2024-08-02

URL	Date	SRC

URL	Date	SRC
https://access.redhat.com/security/cve/CVE-2023-51764	2024-06-10
https://bugzilla.redhat.com/show_bug.cgi?id=2255563	2024-06-10
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JQ5WXFCW2N6G2PH3JXDTYW5PH5EBQEGO	2024-06-10
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFNB44ISVTZC	2024-06-10

Affected Vendors, Products, and Versions

Vendor		Product				Version		Other		Status
Vendor	Product	Version	Other	Status	<-- -->	Vendor	Product	Version	Other	Status
Postfix Search vendor "Postfix"		Postfix Search vendor "Postfix" for product "Postfix"				< 3.5.23 Search vendor "Postfix" for product "Postfix" and version " < 3.5.23"		-		Affected
Postfix Search vendor "Postfix"		Postfix Search vendor "Postfix" for product "Postfix"				>= 3.6.0 < 3.6.13 Search vendor "Postfix" for product "Postfix" and version " >= 3.6.0 < 3.6.13"		-		Affected
Postfix Search vendor "Postfix"		Postfix Search vendor "Postfix" for product "Postfix"				>= 3.7.0 < 3.7.9 Search vendor "Postfix" for product "Postfix" and version " >= 3.7.0 < 3.7.9"		-		Affected
Postfix Search vendor "Postfix"		Postfix Search vendor "Postfix" for product "Postfix"				>= 3.8.0 < 3.8.4 Search vendor "Postfix" for product "Postfix" and version " >= 3.8.0 < 3.8.4"		-		Affected
Fedoraproject Search vendor "Fedoraproject"		Fedora Search vendor "Fedoraproject" for product "Fedora"				38 Search vendor "Fedoraproject" for product "Fedora" and version "38"		-		Affected
Fedoraproject Search vendor "Fedoraproject"		Fedora Search vendor "Fedoraproject" for product "Fedora"				39 Search vendor "Fedoraproject" for product "Fedora" and version "39"		-		Affected
Redhat Search vendor "Redhat"		Enterprise Linux Search vendor "Redhat" for product "Enterprise Linux"				8.0 Search vendor "Redhat" for product "Enterprise Linux" and version "8.0"		-		Affected
Redhat Search vendor "Redhat"		Enterprise Linux Search vendor "Redhat" for product "Enterprise Linux"				9.0 Search vendor "Redhat" for product "Enterprise Linux" and version "9.0"		-		Affected