Red Hat Bugzilla – Bug 186057
CVE-2006-1242 Linux zero IP ID vulnerability?
Last modified: 2014-06-18 04:28:53 EDT
Interesting behaviour of some Linux kernels that may be exploited by a remote
attacker to abuse the ID field of IP packets, effectively bypassing the zero IP
ID in DF packets countermeasure implemented since 2.4.8 (IIRC).
The code paths for sending TCP packets when we have a socket and when
we don't have one are different, and in fact this is unavoidable.
When we send a reset because we don't have a TCP socket that matches,
we have to use tcp_v4_send_reset(), which uses the ip_send_reply()
framework using the system-wide "tcp_socket" that is used for sending
packets when we have no associated socket.
SYN+ACK responses, go through yet another interface, ip_build_and_send_pkt()
We could pass a flag into ip_build_and_send_pkt() to tell it to not use a
non-zero IP ID when the DF bit is set. Actually, scratch that, it should be
using the function "ip_select_ident_more()" just like ip_build_xmit() does.
That would solve the problem.
FWIW I don't see this as much of a real security problem, and by fixing it
we'll make Linux versions even more specifically identifyable remotely :)
According to Chris Wright the latest vanilla kernel contains a fix for it:
Right, I pushed that to 2.6.17 and 2.6.x -stable.
Vanilla 2.4.x does not have the problem, but our RHEL3 2.4.x does
because it contains the IPSEC backport.
RHEL4 is not vulnerable to this with the default firewall enabled, at least not
the case documented. Naturally we should include the fix for cases where it is
committed in stream U4 build 34.14. A test kernel with this patch is available
This issue is on Red Hat Engineering's list of planned work items
for the upcoming Red Hat Enterprise Linux 4.4 release. Engineering
resources have been assigned and barring unforeseen circumstances, Red
Hat intends to include this item in the 4.4 release.
Patch is in -42.EL.
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.