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===========================================================================
AUSCERT External Security Bulletin Redistribution
ESB-2001.099 -- OpenBSD Security Advisory
Buffer overrun in IPSEC AH handling
5 March 2001
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: IPSEC
Vendor: OpenBSD
Impact: Denial of Service
Root Compromise
Access Required: Remote
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- ----------------------------------------------------------------------------
OpenBSD Security Advisory
March 2, 2001
Buffer overrun in IPSEC AH handling
- ----------------------------------------------------------------------------
SYNOPSIS
Due to insufficient checks in the IPSEC Authentication Header IPv4 option
handling a buffer overrun is possible if an AH packet is sent with a
truncated IPv4 option. This can lead to a remote DoS and possibly
root privileges.
For a system to be vulnerable, an administrator must have enabled the
net.inet.ah.enable sysctl(8) value.
A fix for this problem was committed on February 20, 2001.
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AFFECTED SYSTEMS
This vulnerability affects OpenBSD versions through 2.8.
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RESOLUTION
OpenBSD does not ship with IPSEC AH handling enabled by default. If you are
using it, please disable it by entering the command:
# sysctl -w net.inet.ah.enable=0
Then, apply the fix below to your OpenBSD 2.8 source tree. The patch is also
available at http://www.openbsd.org/errata.html (023).
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CREDITS
This vulnerability was first reported and fixed by Jun-ichiro itojun Hagino
(itojun@openbsd.org). This patch has also been applied to the stable branch.
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REFERENCES
Security and errata,
http://www.openbsd.org/security.html
http://www.openbsd.org/errata.html
- ----------------------------------------------------------------------------
OPENBSD 2.8 PATCH
Apply by doing
cd /usr/src
patch -p0 <023_ip_ah.patch
And then rebuild your kernel.
Index: sys/netinet/ip_ah.c
===================================================================
RCS file: /cvs/src/sys/netinet/ip_ah.c,v
retrieving revision 1.45
retrieving revision 1.46
diff -u -r1.45 -r1.46
- --- sys/netinet/ip_ah.c 2000/11/17 04:15:42 1.45
+++ sys/netinet/ip_ah.c 2001/02/20 06:48:06 1.46
@@ -253,6 +253,17 @@
/* IPv4 option processing */
for (off = sizeof(struct ip); off < skip;)
{
+ if (ptr[off] == IPOPT_EOL || ptr[off] == IPOPT_NOP ||
+ off + 1 < skip)
+ ;
+ else
+ {
+ DPRINTF(("ah_massage_headers(): illegal IPv4 option length for option %d
", ptr[off]));
+ ahstat.ahs_hdrops++;
+ m_freem(m);
+ return EINVAL;
+ }
+
switch (ptr[off])
{
case IPOPT_EOL:
@@ -268,10 +279,10 @@
case 0x86: /* Commercial security */
case 0x94: /* Router alert */
case 0x95: /* RFC1770 */
- - /* Sanity check for zero-length options */
- - if (ptr[off + 1] == 0)
+ /* Sanity check for option length */
+ if (ptr[off + 1] < 2)
{
- - DPRINTF(("ah_massage_headers(): illegal zero-length IPv4 option %d
", ptr[off]));
+ DPRINTF(("ah_massage_headers(): illegal IPv4 option length for option %d
", ptr[off]));
ahstat.ahs_hdrops++;
m_freem(m);
return EINVAL;
@@ -282,6 +293,15 @@
case IPOPT_LSRR:
case IPOPT_SSRR:
+ /* Sanity check for option length */
+ if (ptr[off + 1] < 2)
+ {
+ DPRINTF(("ah_massage_headers(): illegal IPv4 option length for option %d
", ptr[off]));
+ ahstat.ahs_hdrops++;
+ m_freem(m);
+ return EINVAL;
+ }
+
/*
* On output, if we have either of the source routing
* options, we should swap the destination address of
@@ -296,10 +316,10 @@
/* Fall through */
default:
- - /* Sanity check for zero-length options */
- - if (ptr[off + 1] == 0)
+ /* Sanity check for option length */
+ if (ptr[off + 1] < 2)
{
- - DPRINTF(("ah_massage_headers(): illegal zero-length IPv4 option %d
", ptr[off]));
+ DPRINTF(("ah_massage_headers(): illegal IPv4 option length for option %d
", ptr[off]));
ahstat.ahs_hdrops++;
m_freem(m);
return EINVAL;
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