CVE-2023-51764: 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.
Overview
- Severity
- Medium (CVSS 5.3)
- CVSS Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Exploit Status
- Not Exploited
- Patch Tuesday
- 2023-Dec
- Released
- 2024-01-06
- Last Updated
- 2026-02-18
- EPSS Score
- 2.60% (percentile: 83.7%)
FAQ
Is Azure Linux the only Microsoft product that includes this open-source library and is therefore potentially affected by this vulnerability?
One of the main benefits to our customers who choose to use the Azure Linux distro is the commitment to keep it up to date with the most recent and most secure versions of the open source libraries with which the distro is composed. Microsoft is committed to transparency in this work which is why we began publishing CSAF/VEX in October 2025. See this blog post for more information. If impact to additional products is identified, we will update the CVE to reflect this.
Detection & Weaponization (1 sources)
Maturity: Exploit
- GitHub PoC: 3 repositories
Affected Products (4)
Other
- 19749-17086
- 18197-16823
- 18198-17084
- 19753-17084
Revision History
- 2024-01-06: Information published.
- 2024-06-30: Information published.
- 2026-02-18: Information published.