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smtp: Validate mail transaction and disable SMTP analyzer if excessive

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An invalid mail transaction is determined as

* RCPT TO command without a preceding MAIL FROM
* a DATA command without a preceding RCPT TO

and logged as a weird.

The testing pcap for invalid mail transactions was produced with a Python
script against a local exim4 configured to accept more errors and unknown
commands than 3 by default:

    # exim4.conf.template
    smtp_max_synprot_errors = 100
    smtp_max_unknown_commands = 100

See also: https://www.rfc-editor.org/rfc/rfc5321#section-3.3
This commit is contained in:
Arne Welzel 2023-03-23 17:13:52 +01:00
parent 0eccd8a7a2
commit b8dc6ad120
14 changed files with 1649 additions and 1506 deletions
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2
scripts/base/frameworks/notice/weird.zeek
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@ -205,6 +205,8 @@ export {
["RST_with_data"] = ACTION_LOG,
["SSL_many_server_names"] = ACTION_LOG,
["simultaneous_open"] = ACTION_LOG_PER_CONN,
["smtp_mail_transaction_invalid"] = ACTION_LOG_PER_CONN,
["smtp_excessive_invalid_mail_transactions"] = ACTION_LOG_PER_CONN,
["spontaneous_FIN"] = ACTION_IGNORE,
["spontaneous_RST"] = ACTION_IGNORE,
["SMB_parsing_error"] = ACTION_LOG,