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GitHub 對抗 TCP SYN Flood 的方式:synsanity

GitHub 提出了自己對抗 TCP SYN Floord 的方式:「SYN Flood Mitigation with synsanity」。

synsanity 是一個 netfilter (iptables) 用的 target,利用現有的理論阻擋 TCP SYN Flood 這種 DDoS:

synsanity is a netfilter (iptables) target for high performance lockless SYN cookies for SYN flood mitigation, as used in production at GitHub.

前人的作法 (SYNPROXY) 以 module 形式運作,需要過濾每一個封包,而這在 GitHub 這種規模上會導致效能不足並且 kernel panic:

This is quite an intrusive way of solving the problem since it touches every packet during the entire connection, but it does successfully mitigate SYN floods. Unfortunately we found that in practise under our load and with the amount of malformed packets we receive, it quickly broke down and caused a kernel panic.

GitHub 所開發的 synsanity 則是透過 netfilter (iptables) 的 target,只處理 initial packets,在撰寫的時候考慮多 CPU 的 lock 問題:

在 Cisco Router 上被植入的後門

FireEye 發表了一篇在 Cisco Router 上發現被植入的後門:「SYNful Knock - A Cisco router implant - Part I」。

發現這些被植入的 router 被散佈在四個地區:

Mandiant can confirm the existence of at least 14 such router implants spread across four different countries: Ukraine, Philippines, Mexico, and India.

包括了這幾個型號:

  • Cisco 1841 router
  • Cisco 2811 router
  • Cisco 3825 router

後門的特性是使用特殊的封包啟動:

SYNful Knock is a stealthy modification of the router's firmware image that can be used to maintain persistence within a victim's network. It is customizable and modular in nature and thus can be updated once implanted. Even the presence of the backdoor can be difficult to detect as it uses non-standard packets as a form of pseudo-authentication.

最主要的重點是把記憶體保護機制關閉 (都變成 RW):

The malware forces all TLB Read and Write attributes to be Read-Write (RW). We believe this change is made to support the hooking of IOS functions by loaded modules.

文後也有提到 Cisco 的文章,如何 dump image 分析:「Offline Analysis of IOS Image Integrity」。

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