Mandrake alert: temporary fix for netfilter information leak

Posted by dave on May 9, 2002 8:40 AM EDT
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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.

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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. ________________________________________________________________________

References: ________________________________________________________________________

Updated Packages:

None currently available. ________________________________________________________________________

Bug IDs fixed (see 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 update.

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 visiting:

If you want to report vulnerabilities, please contact ________________________________________________________________________

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