Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"0x00 背景簡介","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"CDN(Content Delivery Network) 是雲服務廠商提供的一種Web內容加速分發服務。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於攻擊者來說，CDN提供了大量分佈於全球各地的邊緣節點IP，並且可以將源服務器隱藏在CDN節點之後，所以CDN非常適合被用於保護C2的通信。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文介紹了我們在某些CDN實現中發現的一些特性，以及如何利用這些特性隱藏C2通信流量，我們將這種新型的基於CDN的隱蔽通信方法稱爲Domain Borrowing。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"該研究已經發表在Black Hat Asia 2021。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"0x01 歷史研究","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"Domain Fronting","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Domain Fronting[1]是Fifield David等研究人員在2015年提出的一種基於CDN的隱蔽通信方法，該方法至今仍被廣泛應用於真實APT攻擊和紅藍對抗中。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Domain Fronting的工作原理如下圖所示，主要利用了CDN轉發HTTPS請求時的特性。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/63/63c41590c786fa54760e3e847630c91e.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在處理HTTPS請求時，CDN會首先將它解密，並根據HTTP Host的值做請求轉發。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果客戶端想要訪問一個非法網站forbidden.com，它可以使用一個CDN上的合法的域名allow.com作爲SNI, 然後使用forbidden.com作爲HTTP Host與CDN進行HTTPS通信。之後，CDN會將HTTP請求重新封裝，併發往forbidden.com的源服務器。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這種情況下，客戶端實際通信的對象是forbidden.com，但在流量監控設備看來，客戶端是在與allow.com通信，即客戶端將流量成功僞裝成了與allow.com通信的流量。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Domain Fronting也有一些侷限性。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Domain Fronting流量的一個顯著特點是SNI和Host不相等。企業的防守方可以部署HTTPS流量解密設備，並對比流量中的SNI和Host是否相等，如果不相等則說明是該流量是Domain Fronting流量。這也是MITRE ATT&CK[2]中建議的檢測方式。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"並且，隨着該技術不斷在真實網絡攻擊中被使用，雲廠商也逐漸意識到了Domain Fronting的危害，目前Cloudflare、AWS CloudFront、Google Cloud CDN等廠商也都紛紛禁用了這種隱蔽通信方法。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"Domain Hiding","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Domain Hiding[2]是Erik Hunstad在DEFCON28上提出的隱蔽通信方法，這種方法主要依賴於TLSv1.3和ESNI。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/87/874de7f64271a97f07cd6ba67de09af1.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ESNI是IETF的一個草案，目前只有Cloudflare CDN支持該標準。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通信的客戶端可以從_esni.forbidden.com的TXT記錄中獲取密鑰，並使用該密鑰加密SNI，在HTTPS Client Hello中即可使用加密後的SNI即ESNI與CDN進行通信。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"因爲DNS查詢可以通過DNS over TLS/HTTPS進行，所以整個HTTPS通信流量中不會出現明文的forbidden.com。流量監控設備也就無法識別該流量是否爲非法流量。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Erik Hunstad還發現Cloudflare處理ESNI的一個特性，如果Client Hello裏同時出現SNI和ESNI， Cloudflare會忽略SNI字段，使用ESNI完成接下來的通信過程。這樣攻擊者在使用ESNI通信時，就可以將SNI設置爲一個高信譽的的域名來僞裝通信流量。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Domain Hiding也存在一些侷限性。一方面，Cloudflare現在已經不支持Client Hello裏同時出現SNI和ESNI。另一方面，爲了進行流量審查，很多企業甚至國家級防火牆會直接禁止使用ESNI通信。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"0x02 Domain Borrowing","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對攻擊者來說，一個理想的C2通信流量需要滿足以下幾個條件","attrs":{}}]},{"type":"numberedlist","attrs":{"start":null,"normalizeStart":1},"content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"擁有大量IP地址供C2 agent連接","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"使用高信譽的的域名和合法的HTTPS證書","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"即使HTTPS流量可以被解密，解密後的流量也應該與正常流量高度相似，特別是SNI==Host","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"通信協議不依賴於特殊協議標準","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"通信方式不在特殊地區受限制","attrs":{}}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面將詳細介紹我們在某些CDN實現中發現的一些特性，以及如何利用這些特性滿足一個理想C2的隱蔽通信需求。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在HTTPS CDN的工作流程中，DNS只是用於尋找CDN邊緣節點，並不直接參與HTTPS通信。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以客戶端可以直接拋棄DNS解析流程，或者使用另一個加速域名cdn.b.com做DNS解析, 然後使用cdn.a.com作爲SNI/Host與CDN邊緣節點通信。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/46/462ed5d6b25f86e262b9b850192b1741.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"爲了僞裝C2通信流量，需要保證流量中SNI和Host爲高信譽度域名，也就需要我們具備在CDN上註冊高信譽度域名的能力。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們調研了國外常見CDN加速域名註冊時的域名歸屬認證機制，結果如下圖所示。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/67/678a258f687261635439560e4a5e7f2e.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Azure CDN使用DNS CNAME記錄驗證域名歸屬，Cloudflare使用DNS NS記錄驗證域名歸屬，使用者配置相應的DNS記錄後纔可以使用CDN服務。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"AWS CloudFront使用域名的HTTPS證書來驗證域名歸屬權，使用者需要提供域名的合法HTTPS證書纔可使用CDN服務。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Google Cloud CDN的AnyCast機制需要使用者直接將加速域名解析配置爲Google Cloud CDN指定的某個固定IP，雖然AnyCast機制的目的不是爲了進行域名歸屬驗證，但是確實達到了歸屬驗證的效果。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Fastly，StackPath，KeyCDN，CDN77和CDNSun則不存在域名歸屬驗證，攻擊者可以在這些CDN上任意註冊高信譽度域名的加速服務, 如下圖所示。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d8/d86f7e00b647b0bd5611fb89e39abca9.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"以www.blackhat.com爲例，雖然我們可以在上述CDN中註冊該域名的CDN加速服務，但是我們並沒有這個域名的合法HTTPS證書","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當CDN無法找到SNI中的域名對應的證書時，通常有兩種處理邏輯","attrs":{}}]},{"type":"numberedlist","attrs":{"start":null,"normalizeStart":1},"content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"大多數CDN會返回一個默認的證書給客戶端","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"少數CDN會直接斷開與客戶端的TCP連接","attrs":{}}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如下圖所示，Fastly CDN會返回default.ssl.fastly.net的證書給客戶端","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2b/2b8002512eba12a5551ec5e8b3c53349.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在這種情況下，客戶端可以選擇忽略HTTPS證書驗證並與CDN邊緣節點進行HTTPS通信","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這時HTTPS流量中SNI == Host == www.blackhat.com，可以繞過對Domain Fronting的檢測","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"雖然default.ssl.fastly.net證書比自簽名證書可信度要高，但是對於這個HTTPS連接來說這仍然是一個非法的證書","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那麼應該如何獲取高信譽度域名的合法的證書？最簡單的方法就是通過漏洞","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果攻擊者可以獲取目標站點的RCE或者任意文件下載，攻擊者可以直接獲得域名的證書和私鑰","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果攻擊者發現了目標站點的RCE、subdomain takeover、任意文件上傳（尤其是雲存儲的任意文件上傳）等漏洞，攻擊者可以通過HTTP驗證（.well-known）的方式申請目標站點域名的新的證書","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"並且由於證書的有效期比較長，在站點漏洞被修復後，攻擊者申請的證書可能仍然是有效的","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/27/27eabd10abc0b9d8b234e9e445b8d78d.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ppe.verify.microsoft.com的subdomain takeover漏洞（該漏洞由作者一個朋友發現）已經被修復，但是申請下來的證書仍然有效","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"因爲AWS CloudFront僅通過HTTPS證書來做域名歸屬驗證，所以我們拿到一個合法的證書之後就可以在AWS CloudFront上註冊該域名的CDN服務","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f2/f27ba690d47fe7485d4cd295fb8d888a.png","alt":"Domain Borrowing: 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案例：繞過Palo Alto防火牆","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Palo Alto Firewall PAN-VM是Palo Alto的下一代防火牆產品，支持很多優秀的特性，比如SSLv3.0-TLSv1.3的流量解密和Anti-Spyware功能。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對SSL解密功能支持的算法如下圖所示","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5c/5c650944ca6ad8c74e7c1e645250ccef.png","alt":"Domain Borrowing: 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Signatures[4]。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Anti-Spyware Evasion Signatures包含兩條檢測規則Suspicious HTTP Evasion Found和Suspicious TLS Evasion Found","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/46/46b5e0bb0dfbf0b436db3af2d0113491.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Suspicious HTTP Evasion Found用於檢測HTTP Host的DNS解析結果是否與通信目的IP地址相同","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Suspicious HTTPS Evasion Found用於檢測HTTPS SNI的DNS解析結果是否與通信目的IP地址相同","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以理論上Anti-Spyware Evasion Signatures是可以檢測Domain Borrowing的。但是我們研究發現，Palo Alto Firewall在這個功能的實現上存在問題。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果防火牆無法解析出SNI和Host域名的IP地址，則這條通信流量會直接通過檢測。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於Domain Borrowing來說，SNI和Host可以被設置爲一個不存在的域名（即該域名沒有IP地址），這樣就可以繞過Palo Alto Firewall的檢測。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"以img.fontawesome.com爲例","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/3a/3af0cd9a767264e101fe8ec14e5e69c1.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"該域名不是一個真實存在的域名，它沒有任何的DNS記錄","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"攻擊者可以在StackPath上註冊img.fontawesome.com的CDN加速服務，並使用img.fontawesome.com作爲SNI和Host，借用StackPath上合法的通配符HTTPS證書*.fontawesome.com進行C2通信。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在檢測設備看來，攻擊者的通信流量就是一個完全合法的高信譽度域名img.fontawesome.com的HTTPS通信流量，並且可以繞過Anti-Spyware Evasion Signatures的檢測。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/a7/a7968c4cc1b12588e2a92d7fa45a96f6.png","alt":"Domain Borrowing: 一種基於CDN的新型隱蔽通信方法（全程乾貨！）","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ab/ab5da14454a25c1453ae843c88b07540.gif","alt":null,"title":"點擊並拖拽以移動","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"該繞過方法已經報告給Palo Alto PSIRT。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"0x05 Covenant Implant Template","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們實現了一個使用Domain Borrowing通信的Covenant[5] Implant Template，希望幫助攻擊方在紅藍對抗中應用Domain Borrowing技術，也希望能夠幫助防守方加強對此類通信流量的檢測能力。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Github Repo: https://github.com/Dliv3/DomainBorrowing","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"0x06 參考資料","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"[1] https://www.icir.org/vern/papers/meek-PETS-2015.pdf[2] https://attack.mitre.org/techniques/T1090/004/[3] https://media.defcon.org/DEF%20CON%2028/DEF%20CON%20Safe%20Mode%20presentations/DEF%20CON%20Safe%20Mode%20-%20Erik%20Hunstad%20-%20Domain%20Fronting%20is%20Dead%20Long%20Live%20Domain%20Fronting.pdf[4] https://docs.paloaltonetworks.com/pan-os/10-0/pan-os-admin/threat-prevention/enable-evasion-signatures.html[5] https://github.com/cobbr/Covenant","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最後在多說幾句：我是一名網絡安全工程師，也是剛開始做自媒體","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"爲了感謝讀者們，我想把我收藏的一些","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"網絡安全/滲透測試學習乾貨","attrs":{}},{"type":"text","text":"貢獻給大家，回饋每一個讀者，希望能幫到你們。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"乾貨主要有：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"①　2000多本網安必看電子書（主流和經典的書籍應該都有了）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"②　PHP標準庫資料（最全中文版）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"③　項目源碼（四五十個有趣且經典的練手項目及源碼）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"④ 網絡安全基礎入門、Linux運維，web安全、滲透測試方面的視頻（適合小白學習）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"⑤ 網絡安全學習路線圖（告別不入流的學習）","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"各位朋友們可以關注+評論一波 然後私信 備註：網安學習  即可免費獲取","attrs":{}}]}]}