Fwd: [is this mbuf problem real?]

[Andre Oppermann]

"Jacques A. Vidrine" wrote:
> 
> Does anyone have time to investigate?  I will try to get more
> information from iDEFENSE.

Looking at the code there are indeed some problems.

 - there seems to be no boundary on how many segments we keep in the
   tcp reassembly queue
 - there seems to be no timeout of overaged fragments (we can drop
   the segments after 1*msl because we don't have SACK and it has
   to be retransmitted anyway since not ACK'ed which happens after
   read from userland).  Possibly it can be dropped earlier after
   we've got x bytes or packets of more segments since it is un-
   likely to receive the missing packet this late except for really
   massive reordering
 - this attack can be made with small packets which consume an mbuf
   cluster anyway

For IP packet reassembly we have global and local limits:

 net.inet.ip.maxfragpackets: 800
 net.inet.ip.maxfragsperpacket: 16

Something like this is needed for TCP as well to cope with this kind
of resource exhaustion attack.

I can fix this stuff but I won't be able to do that in emergency mode.
The first code can be ready after the weekend.  If someone else wants
to takle it earlier/faster tell me.

-- 
Andre


> Cheers,
> --
> Jacques Vidrine / nectar at celabo.org / jvidrine at verio.net / nectar at freebsd.org
> 
> ----- Forwarded message from Baby Peanut <baby_p_nut2 at yahoo.com> -----
> 
> Date: Wed, 18 Feb 2004 06:21:25 -0800 (PST)
> From: Baby Peanut <baby_p_nut2 at yahoo.com>
> To: freebsd-security at freebsd.org
> Subject: is this mbuf problem real?
> Message-ID: <20040218142125.49433.qmail at web41902.mail.yahoo.com>
> 
> BM_207650
> MEDIUM
> Vulnerability
> Version: 1  2/18/2004 at 03:47:29 GMT
> Initial report
>          <https://ialert.idefense.com/KODetails.jhtml?irId=207650>
> ID#207650:
> FreeBSD Memory Buffer Exhaustion Denial of Service Vulnerability
> (iDEFENSE Exclusive): Remote exploitation of a denial of service (DoS)
> vulnerability in FreeBSD's memory buffers (mbufs) could allow attackers
> to launch a DoS attack.
> 
> By sending many out-of-sequence packets, a low bandwidth denial of
> service attack is possible against FreeBSD. When the targeted system
> runs out of memory buffers (mbufs), it is no longer able to accept or
> create new connections.
> 
> Analysis: (iDEFENSE US) Exploitation of this vulnerability requires
> that the targeted system has at least one open TCP port.
> 
> The DoS will last until the port is closed, either by the attacker or
> the target machine.
> 
> Detection: iDEFENSE has confirmed this vulnerability exists in FreeBSD
> 5.1 (default install from media). It is expected that it also exists
> in earlier versions.
> 
> Exploit: iDEFENSE has proof of concept exploit code demonstrating the
> impact of this vulnerability.
> 
> Vulnerability Types: Design Error - Denial of Service
> Prevalence and Popularity: Almost always
> Evidence of Active Exploitation or Probing: No known exploitation or
> spike in probing
> Ease of Exploitation: Remotely Exploitable
> Existence and Availability of Exploit Code: An Exploit exists and is
> closely traded.
> Vulnerability Consequence: Availability
> 
> __________________________________
> Do you Yahoo!?
> Yahoo! Mail SpamGuard - Read only the mail you want.
> http://antispam.yahoo.com/tools
> _______________________________________________
> freebsd-security at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-security
> To unsubscribe, send any mail to "freebsd-security-unsubscribe at freebsd.org"
> 
> ----- End forwarded message -----
> 
> _______________________________________________
> freebsd-net at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-net
> To unsubscribe, send any mail to "freebsd-net-unsubscribe at freebsd.org"