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Home » Security Advisories» NetBSD » pf denial of service

pf denial of service

There is a logical bug in pf's scrub fragment cache, which in certain configurations may lead to a remotely exploitable denial of service attack.

  • Vendor: NetBSD
  • Vendor ID: 2006-004
  • Date: March 28, 2006

Hash: SHA1

NetBSD Security Advisory 2006-004

Topic: Denial of services issues with pf

Version: NetBSD-current: source prior to January 25, 2006
NetBSD 3.0: affected
NetBSD 2.1: not affected
NetBSD 2.0.*: not affected
NetBSD 2.0: not affected
NetBSD 1.6.*: not affected
NetBSD 1.6: not affected

Severity: Denial of service

Fixed: NetBSD-current: January 25, 2006
NetBSD-3-0 branch: January 28, 2006
(3.0.1 will include the fix)
NetBSD-3 branch: January 28, 2006


There is a logical bug in pf's scrub fragment cache, which in certain
configurations may lead to a remotely exploitable denial of service

This vulnerability has been assigned CVE reference CVE-2006-0381.

Technical Details

When 'scrub fragment crop/drop-ovl' is used, certain combinations of fragments
cause double insertion into the fragment cache, which violates an
invariant, and subsequently triggers a kernel panic through KASSERT().

pf is not enabled by default on NetBSD.

Solutions and Workarounds

Do not use 'scrub fragment drop-ovl' or 'scrub fragment crop' rules on NetBSD
systems where pf has been enabled.

For all NetBSD versions, if you are using pf, you need to obtain
fixed kernel sources, rebuild and install the new kernel, and reboot
the system.

The fixed source may be obtained from the NetBSD CVS repository.

The following instructions briefly summarize how to upgrade your
kernel. In these instructions, replace:

ARCH with your architecture (from uname -m), and
KERNCONF with the name of your kernel configuration file.

To update from CVS, re-build, and re-install the kernel:

# cd src
# cvs update -d -P src/sys/dist/pf/net/pf_norm.c
# ./ kernel=KERNCONF
# mv /netbsd /netbsd.old
# cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd
# shutdown -r now

For more information on how to do this, see:

Thanks To

Daniel Hartmeier for notification of the issue and a suggested fix.
Peter Postma for implementing the fix in the NetBSD CVS tree.

Revision History

2006-03-29 Initial release

More Information

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at

Information about NetBSD and NetBSD security can be found at and

Copyright 2006, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2006-004.txt,v 1.7 2006/03/29 11:14:28 adrianp Exp $

Version: GnuPG v1.4.2.2 (NetBSD)


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