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Mandrake Linux Advisory: iptables/kernel

May 09, 2002, 17:29 (4 Talkback[s])


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                Mandrake Linux Security Update Advisory

Package name:           iptables/kernel
Advisory ID:            MDKSA-2002:030
Date:                   May 9th, 2002
Affected versions:      8.0, 8.1, 8.2

Problem Description:

 A problem was discovered with Netfilter Network Address Translation
 (NAT) capabilities.  It was found that iptables can leak information
 about how port forwarding is accomplished in unfiltered ICMP packets.
 When a NAT rule applies to the first packet of a connection, which
 subsequently causes the system to generate an ICMP error message, the
 ICMP error message is transmitted including the translated address.
 This information gives the IP address of the system to which the
 connection would have been forwarded had the error message not been
 generated, exposing information about the netfilter configuration and
 the network topology.

 There is currently no clean fix for this problem, but a fix is being
 worked on.  In the meantime, if you use the NAT capabilities of
 iptables, you can protect yourself by filtering out untracked local
 ICMP packets using the following iptables command:

   iptables -A OUTPUT -m state -p icmp --state INVALID -j DROP

 All kernel patches from iptables < 1.2.6a are vulnerable.  All kernel
 versions from 2.4.4 and up to (at least) 2.4.19-pre6 use a vulnerable
 version.  Thanks to Philippe Biondi for discovering this problem.



Updated Packages:

  None currently available.

Bug IDs fixed (see https://qa.mandrakesoft.com for more information):


To upgrade automatically, use MandrakeUpdate.  The verification of md5
checksums and GPG signatures is performed automatically for you.

If you want to upgrade manually, download the updated package from one 
of our FTP server mirrors and upgrade with "rpm -Fvh *.rpm".  A list of
FTP mirrors can be obtained from:


Please verify the update prior to upgrading to ensure the integrity of
the downloaded package.  You can do this with the command:

  rpm --checksig <filename>

All packages are signed by MandrakeSoft for security.  You can obtain
the GPG public key of the Mandrake Linux Security Team from:


Please be aware that sometimes it takes the mirrors a few hours to 

You can view other update advisories for Mandrake Linux at:


MandrakeSoft has several security-related mailing list services that
anyone can subscribe to.  Information on these lists can be obtained by


If you want to report vulnerabilities, please contact


Type Bits/KeyID     Date       User ID
pub  1024D/22458A98 2000-07-10 Linux Mandrake Security Team