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.

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.

The postfix packages provide a Mail Transport Agent (MTA), which supports protocols like LDAP, SMTP AUTH (SASL), and TLS.

Security Fix(es):

• postfix: SMTP smuggling vulnerability (CVE-2023-51764)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Additional Changes:

For detailed information on changes in this release, see the Rocky Linux 9.5 Release Notes linked from the References section.

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.

The postfix packages provide a Mail Transport Agent (MTA), which supports protocols like LDAP, SMTP AUTH (SASL), and TLS.

Security Fix(es):

• postfix: SMTP smuggling vulnerability (CVE-2023-51764)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Additional Changes:

For detailed information on changes in this release, see the AlmaLinux Release Notes linked from the References section.

• CVE-2023-51764: Improvements for inbound SMTP smuggling defense. Reject or restrict input lines from an SMTP client that end in bare new line. Replace each stray <CR> or <LF> character in message content with a space character, to prevent outbound SMTP smuggling To prevent the SMTP smuggling vulnerability, the option "smtpd_forbid_bare_newline = reject" must be set.

• CVE-2023-51764: fix SMTP smuggling (backport of 2.11.11-smuggling-patch)

• CVE-2023-51764: fix SMTP smuggling (backport of 2.11.11-smuggling-patch)

Postfix has been updated to fix smtp smuggling, an email spoofing attack that involves a composition of email services with specific differences in the way they handle line endings other than <CR><LF>.

These are all security issues fixed in the postfix-3.8.4-2.1 package on the GA media of openSUSE Tumbleweed.

This update for postfix fixes the following issues:

• CVE-2023-51764: Fixed new SMTP smuggling attack (bsc#1218304).

This update for postfix fixes the following issues:

• CVE-2023-51764: Fixed SMTP smuggling attack (bsc#1218304).

This update for postfix fixes the following issues:

• CVE-2023-51764: Prevent SMTP smuggling attack. (bsc#1218304)

Timo Longin discovered that Postfix incorrectly handled certain email line endings. A remote attacker could possibly use this issue to bypass an email authentication mechanism, allowing domain spoofing and potential spamming.

Please note that certain configuration changes are required to address this issue. They are not enabled by default for backward compatibility. Information can be found at https://www.postfix.org/smtp-smuggling.html.

USN-6591-1 fixed vulnerabilities in Postfix. A fix with less risk of regression has been made available since the last update. This update updates the fix and aligns with the latest configuration guidelines regarding this vulnerability.

We apologize for the inconvenience.

Original advisory details:

Timo Longin discovered that Postfix incorrectly handled certain email line endings. A remote attacker could possibly use this issue to bypass an email authentication mechanism, allowing domain spoofing and potential spamming.

Please note that certain configuration changes are required to address this issue. They are not enabled by default for backward compatibility. Information can be found at https://www.postfix.org/smtp-smuggling.html.