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security: postfix SMTP smuggling #3719

@becker-s

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@becker-s

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Something else that requires developers attention

Description

A vulnerability affecting several mail server implementations, including postfix, has been disclosed recently.
See the related postfix documentation page for more details: https://www.postfix.org/smtp-smuggling.html

While a short-term workaround exists, it is only partial:

NOTE: This will stop only the published form of the attack. Other forms exist that will not be stopped in this manner.

Postfix should be updated to a version in which the vulnerability is fixed (3.8.4, 3.7.9, 3.6.13 or 3.5.23) and the new optional feature smtpd_forbid_bare_newline be set to yes. The feature will be enabled by default for postfix >= 3.9.

If the smtpd_forbid_bare_newline feature cannot be enabled for backward-compatibility reasons, you could release a patch version of DMS with one of the patched postfix versions and let users decide whether they want to enable the feature via their local configuration.

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