{"id":26558,"date":"2025-02-11T10:58:55","date_gmt":"2025-02-11T01:58:55","guid":{"rendered":"https:\/\/je1sgh.mydns.jp\/je1sghblog\/?p=26558"},"modified":"2025-02-11T10:58:55","modified_gmt":"2025-02-11T01:58:55","slug":"ipv4%e3%81%aasendmail%e6%8b%92%e5%90%a6%e3%82%8a%e3%81%be%e3%81%99","status":"publish","type":"post","link":"https:\/\/je1sgh.mydns.jp\/je1sghblog\/?p=26558","title":{"rendered":"IPv4\u306asendmail\u62d2\u5426\u308a\u307e\u3059"},"content":{"rendered":"\n

イミフなタイトルですみません😓<\/p>\n\n\n\n

ここ数年，MTAのいくつかのポートを全開にしておくと，たまに同じIPアドレスからメール送信や認証をしようといる不正アクセスがあります．まあ，日に数件で脅威というほどではありません．IPアドレスはたまに変わりますがしばらくは一定なのでブラックリストに登録すればしばらく攻撃されません．<\/p>\n\n\n\n

一方，いろんなIPアドレスから日に数百件不正アクセスを試みる攻撃があります．これはなかなか扱いにくく，不正アクセスをしてきたIPアドレスをブラックリストに登録しても別のIPアドレスから攻めてくるのでただただブラックリストが肥大化するだけで効果がありません．<\/p>\n\n\n\n

そこで考えたのですが，自分の管理するMTAに来るまともなメールは知れているので，IPv4を閉じてしまうことです．まれにIPv6からの攻撃もありますが，ほとんど数百に1つという感じです．まあIPv6も扱えない低脳攻撃者と言うことです．<\/p>\n\n\n\n

その設定をしておくとさすがに攻撃元も徒労と気がつくのかしばらく（数か月）攻撃が止みますので，またもとのIPv4のMTAもオープンな設定にします．<\/p>\n\n\n\n

先ほどまでそのオープンな状態だったのですが，ログを見ると2日前から，いろんなIPから攻めてくる攻撃が始まっていましたので，またIPv4を閉じました．<\/p>\n\n\n\n

もし当サイトへの直通メールを送る方はIPv6で送って下さい1<\/a><\/sup>これだけでやりかたが分かる人はすごいと思います😓<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

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