Security audit 2026-10-17, finding M2, stage 0 - proven on the live server:
Postfix quotes a refused recipient in its reply in internal form (quotes
removed, "; < > =" kept: extract_addr, tok822_internalize), so
RCPT TO:<"; from=<ceo@…> to=<board@…> proto=ESMTP helo=<x>; "@domain>
spelled a whole tail inside the reply, and inboundRejectRe, whose reply
ended at the FIRST "; from=<", took the stranger's sender, recipient and
inbound domain for the row.
Now the reply is greedy and the tail anchored: "; from=<…> to=<…>
proto=\S+", a HELO name holding none of Postfix's NEUTER_CHARACTERS
(smtpd.c:1634, helo_cmd neuters ` <>()\";@`), and one-word SASL fields to
the end of the line (a `.*` SASL tail would have let a quoted MAIL FROM
spell the whole tail). Belt and braces: a reply that still holds
"; from=<" - a line with two tails - makes no row, so neither a recipient
nor an un-neutered HELO name can choose one. The quote/bracket/space
filter on from/to stays.
Tests: TestInboundRecipientCannotWriteTheRow (the live line's shape, and
with a forged MAIL FROM too); TestInboundHeloCannotWriteTheRow now feeds
HELO names as Postfix logs them (neutered) and expects no row for the
un-neutered ones. go test ./internal/logtail on Windows (the three known
Windows-only Follow failures aside).
Docs: security.md § Mail path; CHANGELOG; plan line ticked.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
mixandClaude Opus 5.5
683fdafc6d