PMG: Bypass DMARC check by spoofed envelope sender header
Affected packages
pmg-api
Details
Adding a X-Proxmox-Envelope-From header to a mail confuses pmg-smtp-filter into using the mail-address there, instead of the actual envelope sender for the DMARC alignment check. Sending a mail with valid SPF result from one domain can yield a pass result for the strict DMARC policy of a different domain, effectively bypassing DMARC.
The issue is addressed, by passing the envelope sender address directly to SpamAssassin instead of by adding a X-Proxmox-Envelope-From header before parsing. This also modifies the template for SpamAssassin's local.cf configuration file. If you have a modified /etc/pmg/templates/local.cf.in make sure to adapt it to the removal of envelope_sender_header X-Proxmox-Envelope-From.
The issue was privately reported by Gabriele Caniglia, NetRelay <[email protected]>.
Fixed in
- pmg-api >= 9.1.3
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