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Date: Thu, 3 Aug 2017 04:28:46 +0900
From: "Hector Martin \"marcan\"" <>
Subject: [FD] [No CVE assigned] SMBLoris Windows/Samba SMB service DoS PoC

PoC (runs under Linux):

Original disclosure:

There's a lot of talk about SMBLoris but nobody seems to have written a
public efficient PoC yet, so I gave it a shot. A single instance takes
down a fully patched Windows 10 Pro box with 8GiB of RAM in less than 10

I tried using Scapy initially, but it's dog slow, so I went with C. The
PoC uses raw sockets to bypass the local TCP stack. It supports
attacking from multiple source IPs (not requiring them to be bound to
the adapter). There is rudimentary ARP support (gratuitous only, no real
reply functionality). There is no throttling so some packets may be dropped.

I haven't seen it completely deadlock a Windows machine yet (it keeps
accepting connections and responding to pings), but it renders it
completely unusable during the attack and several minutes after it
ceases, and causes various kinds of persistent breakage (UI restarts,
complete UI crashes, inability to start applications, I/O errors due to
failure to allocate memory in the storage controller driver, etc.) where
the only way to get the system behaving properly again is a hard reboot.

On Samba/Linux it just causes typical recoverable Linux OOM behavior
(modulo some processes getting OOM-killed) since smbd forks for each
connection and consumes memory. This can be mitigated with 'max smb
processes = 1000' in smb.conf.

Hector Martin "marcan" (
Public Key:

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