From fd8339703ccb99fccb95059996001f6734043655 Mon Sep 17 00:00:00 2001 From: "Danilo M." Date: Tue, 8 Sep 2026 16:28:01 +0200 Subject: fix: take the sender domain from the address, not the display name _ADDR_DOMAIN.search() returned the first @domain anywhere in the raw header text. A display name sits before the angle brackets and is attacker-controlled, so it won. Two ways that reached a published report. The sender was misattributed: "Billing at billing@innocent.example" filed the report against a third party who sent nothing. And it defeated the structural guarantee in sender_domains(): the module reads no recipient header, but an attacker who writes the victim's own address into the display name hands it one anyway, and it came back out as a sender domain. parseaddr() parses the header grammar rather than scanning it, so a quoted display name cannot supply the address. leaky.eml's display name now carries the recipient address. The existing test_no_ioc_holds_a_recipient_address assertion catches this class; it was green before only because the fixture used a harmless domain. Co-Authored-By: Claude Opus 5 Claude-Session: https://claude.ai/code/session_019NHaqA1Rz5ybed7wFUeQbK --- tests/fixtures/leaky.eml | 2 +- tests/test_parse.py | 7 +++++++ 2 files changed, 8 insertions(+), 1 deletion(-) (limited to 'tests') diff --git a/tests/fixtures/leaky.eml b/tests/fixtures/leaky.eml index 840ce6d..f98d191 100644 --- a/tests/fixtures/leaky.eml +++ b/tests/fixtures/leaky.eml @@ -5,7 +5,7 @@ Received: from sender.example.invalid (unknown [203.0.113.42]) by mx.example.org (Postfix) with ESMTP id JJJ11 for ; Tue, 8 Sep 2026 16:00:01 +0200 (CEST) Return-Path: -From: "Billing at billing@innocent.example" +From: "Billing at you@example.org" To: Subject: Confirm now Message-ID: diff --git a/tests/test_parse.py b/tests/test_parse.py index 49fc41e..de78b5a 100644 --- a/tests/test_parse.py +++ b/tests/test_parse.py @@ -108,6 +108,13 @@ class TestSenderDomains(unittest.TestCase): domains = parse.sender_domains(load("simple.eml")) self.assertNotIn("example.org", domains.values()) + def test_the_domain_comes_from_the_address_not_the_display_name(self): + # A display name is attacker-controlled and sits BEFORE the angle + # brackets, so a regex scanning the raw header finds it first. Doing + # that files the report against whoever the attacker named. + domains = parse.sender_domains(load("leaky.eml")) + self.assertEqual(domains["from"], "sender.example.invalid") + class TestAuthResults(unittest.TestCase): def test_verdicts_are_read_as_the_server_recorded_them(self): -- cgit v1.2.3