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Postfix through 3.8.5 can be used for SMTP smuggling because it accepts the non-standard SMTP DATA termination sequence <LF>.<CR><LF>. This differs from the RFC 5321 end-of-data sequence, <CR><LF>.<CR><LF>, and may be interpreted differently by a downstream SMTP server. An attacker can exploit this parser discrepancy to cause Postfix to treat part of a transaction as a new SMTP message, injecting a message with a spoofed MAIL FROM value.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository provides a proof-of-concept exploit for CVE-2023-51764, a vulnerability in Postfix SMTP servers known as SMTP Smuggling. The exploit consists of a single Expect script ('cve-2023-51764.sh') and a README file. The script automates an SMTP session to a target mail server (specified by FQDN and port), sending an initial legitimate email followed by several additional emails with spoofed senders and recipients within the same session. This technique exploits the vulnerability to bypass SPF, DKIM, and DMARC checks for the inner emails, demonstrating the risk of email spoofing via SMTP smuggling. The README provides usage instructions, requirements, and references to further information. The exploit is a functional proof-of-concept and does not include weaponized or customizable payloads beyond the demonstration of the vulnerability.
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6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Referenced only as a prior vulnerability in the same SMTP-smuggling vulnerability class.
A prior SMTP-smuggling vulnerability referenced solely as being in the same vulnerability class as CVE-2026-33604.
SMTP smuggling vulnerability affecting Postfix, caused by differing interpretations of SMTP end-of-data sequences, which can allow a second email to be smuggled through the same SMTP connection and bypass SPF, DKIM, and DMARC protections.
SMTP smuggling vulnerability affecting Postfix, caused by differing SMTP end-of-data parsing that can allow a second email to be smuggled over the same SMTP connection and bypass SPF, DKIM, and DMARC protections.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.