CVE-2023-51764

MEDIUM
5.3
CVSS Score
Published: December 24, 2023 at 12:00 AM UTC
Updated: October 8, 2026 at 09:17 PM UTC
3 products affected across 3 vendorsFedoraEnterprise LinuxPostfix

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Severity
MEDIUM5.3
Exploit prediction
EPSS 3%
SSVC
No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 3.5.233.6.0 ≤ v < 3.6.133.7.0 ≤ v < 3.7.93.8.0 ≤ v < 3.8.4*
Affected range stops below 3.5.23, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.6.13, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.7.9, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.8.4, so it looks safe — our inference, not a vendor statement

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-345

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