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
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.
None currently available.
Bug IDs fixed (see https://qa.mandrakesoft.com for more information):
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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
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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
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Please be aware that sometimes it takes the mirrors a few hours to
You can view other update advisories for Mandrake Linux at:
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If you want to report vulnerabilities, please contact
Type Bits/KeyID Date User ID
pub 1024D/22458A98 2000-07-10 Linux Mandrake Security Team