Enabling SecureNAT dhcp server in virtual hub exposes DHCP requests in local bridge? · SoftEtherVPN/SoftEtherVPN#325

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bughelp wantedsecurityvulnerability

描述

I have SoftEtherVPN server with:

a virtual hub for local LAN bridge.
17 closed virtual hubs for customers (SecureNAT DHCP server is enabled)

It seems to continuously send 17 dhcp requests into LAN per 2 seconds.

The syslog from BUFFALO router:

[2017/05/18 9:20:11]<14>May 18 09:20:12 syslog: [DHCPS Request incoming from securenat-da50b12b8030(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:12 syslog: [DHCPS Sending ACK to 192.168.2.27]
[2017/05/18 9:20:16]<14>May 18 09:20:12 syslog: [DHCPS Request incoming from securenat-da4b3db9a03a(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:12 syslog: [DHCPS Sending ACK to 192.168.2.98]
[2017/05/18 9:20:16]<14>May 18 09:20:12 syslog: [DHCPS Request incoming from securenat-da27a101f809(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:12 syslog: [DHCPS Sending ACK to 192.168.2.100]
[2017/05/18 9:20:16]<14>May 18 09:20:12 syslog: [DHCPS Request incoming from securenat-da8a4ddc7317(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:12 syslog: [DHCPS Sending ACK to 192.168.2.78]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da349aac10f2(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.88]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da239d215ce8(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.94]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da47cd8d54fe(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.85]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da4380cb8ce5(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.25]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-dae5a40d4430(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.33]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-daad45651ed1(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.31]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da871b4ca5e5(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.93]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da09d62e76d1(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.80]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da3e3284a753(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.32]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Request incoming from securenat-da545ac308e9(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:13 syslog: [DHCPS Sending ACK to 192.168.2.47]
[2017/05/18 9:20:16]<14>May 18 09:20:14 syslog: [DHCPS Request incoming from securenat-da62aa5a4aa9(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:14 syslog: [DHCPS Sending ACK to 192.168.2.23]
[2017/05/18 9:20:16]<14>May 18 09:20:14 syslog: [DHCPS Request incoming from securenat-dabed6be41c4(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:14 syslog: [DHCPS Sending ACK to 192.168.2.71]
[2017/05/18 9:20:16]<14>May 18 09:20:14 syslog: [DHCPS Request incoming from securenat-da8f880390d9(len:22)]
[2017/05/18 9:20:16]<14>May 18 09:20:14 syslog: [DHCPS Sending ACK to 192.168.2.99]

FYI it says DHCPREQUEST is thrown when secureNAT is enabled on vpnserver. Increasing dhcp_renew_interval will mitigate frequency.

http://tamae.2ch.net/test/read.cgi/sec/1114435660/l50

367名無しさん＠お腹いっぱい。2014/02/13(木) 23:26:55.48
vpnserver が secureNAT 使用時に DHCPREQUEST 投げまくるので調べてみた。 
Cedar/Virtual.c　の　dhcp_renew_interval を　* 1000 することで解決するみたい

貢獻者指南

技術棧: c
領域: backendsecurity
議題類型: bug
難度: 3
預計時間: 1-3 hours
活動狀態: stale
清晰度: mostly clear
前置要求: C programmingDHCP protocolSoftEtherVPN internals
新手友善度: 40
研究方向: The issue describes SecureNAT DHCP servers sending excessive DHCP requests into the local bridge. A user on 2ch suggests modifying `dhcp renew interval` in `Cedar/Virtual.c` (multiply by 1000). The fix likely involves changing the interval value in this file to reduce frequency. Confirm the exact location and test for side effects.