IPv4 forwarding doesn't consult inbound SPD in KAME-derived IPsec Greg Troxel <gdtat_private> Bill Chiarchiaro <wjcat_private> 2002-02-24 SUMMARY NetBSD 1.5.2 and -current, FreeBSD 4.5 and -current, and the KAME versions of NetBSD and FreeBSD fail to perform inbound policy checks on packets which are forwarded, in violation of RFC2401 sections 4.4.1 and 5.2.1 (steps 3 and 4). NetBSD, FreeBSD, and KAME have already committed changes to address this problem. The typical case where one might care is at a Security Gateway where packets from a peer gateway are required to be ESP in order to provide confidentiality and integrity. If the SG peer fails to use ESP, confidentiality is lost. If the local SG follows RFC2401 and performs inbound SPD checking, the packet will be determined to require ESP and be dropped. However, with the present code, no SPD check is performed, and the packets -- possibly forged -- will be forwarded, presumably to hosts relying on the SG. DETAILS The defect was observed in attempting to control network access from an 802.11 LAN by requiring tunnel-mode ESP of all traffic from the wireless host, with tunnel endpoints of the host and an SG with a wired interface and an 802.11 interface. We observed that non-ESP packets (emitted due to configuration errors) were forwarded by the SG; this is a real failure that caused a security policy to be violated, although in a situation with no adverse consequences. The policy called for ESP for confidentiality over 802.11 and access control to the wired network and resulting Internet connection. With the defect, an attacker could have injected packets into the Internet, but not received packets because the outbound SPD check on the SG functioned correctly. Examine src/sys/netinet/ip_input.c, and follow the code from the call to ip_forward(). Note that inbound SPD check is done only for packets for this host, and only for protocols with PR_LASTHDR; the check is deferred to protocol implementation to enable per-socket policy. Patches that fix (at least in the normal case) the problem for IPv4 are enclosed for fairly recent points along NetBSD's netbsd-1-5 branch and FreeBSD's RELENG_4 branch. The KAME versions of ip_input.c are very similar. These patches are probably not sufficient; the check should probably be in ip_forward (aligned with the IPv6 implementation). A more careful analysis is needed to consider all the code paths; we have not considered interaction of inbound SPD checks with tunneling (e.g. gif) and other features. In particular, forwarding of packets via source routing options seems to be handled incorrectly. OTHER SYSTEMS FreeBSD RELENG_4 and NetBSD netbsd-1-5 appear to perform this check for IPv6 in ip6_forward; KAME has had the relevant code since 1999-09-01. OpenBSD began to perform this check as of revision 1.58 of src/sys/netinet/in_input.c on 2000-09-01; we have not tested OpenBSD. DETAILS We give details for a simple setup with alice and bob on two networks connected by two SGs alice-gw and bob-gw, nominally intended to use tunnel-mode ESP for all traffic between the networks. (We present results from an actual experiment, but with the IP addresses obscured and irrelevant traffic removed.) 10.1.1.48/28 is Alice's network, and 10.1.1.64/28 is Bob's (both red). 10.1.1.32/28 is the black network connecting Alice (.34) and Bob (.35). alice-gw SPD # to/from bob spdadd 10.1.1.48/28[any] 10.1.1.64/28[any] any -P out ipsec esp/tunnel/10.1.1.34-10.1.1.35/require ; spdadd 10.1.1.64/28[any] 10.1.1.48/28[any] any -P in ipsec esp/tunnel/10.1.1.35-10.1.1.34/require ; bob-gw SPD # to/from alice # intentional misconfiguration for testing - no ESP to alice spdadd 10.1.1.64/28[any] 10.1.1.48/28[any] any -P out none ; #spdadd 10.1.1.64/28[any] 10.1.1.48/28[any] any # -P out ipsec esp/tunnel/10.1.1.35-10.1.1.34/require ; spdadd 10.1.1.48/28[any] 10.1.1.64/28[any] any -P in ipsec esp/tunnel/10.1.1.34-10.1.1.35/require ; EXAMPLE WITH THE INCORRECT CODE With NetBSD along netbsd-1-5 as of 2001-11-26, examining the black network at alice-gw, we see a cleartext SYN, followed by alice-gw initiating IKE due to the response from alice, followed by a retransmitted SYN and the reset in ESP: 09:44:45.258912 bob.65514 > alice.8001: S 406012389:406012389(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2214891 0> 09:44:45.260843 alice-gw.isakmp > bob-gw.isakmp: isakmp: phase 1 I ident: (sa: doi=ipsec situation=identity (p: #1 protoid=isakmp transform=1 (t: #1 id=ike (type=lifetype value=sec)(type=lifeduration value=0258)(type=enc value=3des)(type=auth value=rsa sig)(type=hash value=sha1)(type=group desc value=modp1024)))) 09:44:45.262261 bob-gw.isakmp > alice-gw.isakmp: isakmp: phase 1 R ident: (sa: doi=ipsec situation=identity (p: #1 protoid=isakmp transform=1 (t: #1 id=ike (type=lifetype value=sec)(type=lifeduration value=0258)(type=enc value=3des)(type=auth value=rsa sig)(type=hash value=sha1)(type=group desc value=modp1024)))) (vid: len=16) 09:44:45.345226 alice-gw.isakmp > bob-gw.isakmp: isakmp: phase 1 I ident: (ke: key len=128) (nonce: n len=16) (vid: len=16) 09:44:45.426774 bob-gw.isakmp > alice-gw.isakmp: isakmp: phase 1 R ident: (ke: key len=128) (nonce: n len=16) (vid: len=16) (cr: len=1 type=x509sign) 09:44:45.545348 alice-gw.isakmp > bob-gw.isakmp: isakmp: phase 1 I ident[E]: [|id] 09:44:45.576906 bob-gw.isakmp > alice-gw.isakmp: isakmp: phase 1 R ident[E]: [|id] 09:44:45.577171 bob-gw.isakmp > alice-gw.isakmp: isakmp: phase 2/others R inf[E]: [|hash] 09:44:45.582749 alice-gw.isakmp > bob-gw.isakmp: isakmp: phase 2/others I inf[E]: [|hash] 09:44:46.588822 alice-gw.isakmp > bob-gw.isakmp: isakmp: phase 2/others I oakley-quick[E]: [|hash] 09:44:46.590693 bob-gw.isakmp > alice-gw.isakmp: isakmp: phase 2/others R oakley-quick[E]: [|hash] 09:44:46.591449 alice-gw.isakmp > bob-gw.isakmp: isakmp: phase 2/others I oakley-quick[E]: [|hash] 09:44:51.217057 bob.65514 > alice.8001: S 406012389:406012389(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2214902 0> 09:44:51.217686 alice-gw > bob-gw: ESP(spi=29712172,seq=0x1) On the Alice red network we see the SYNs and the response (a TCP reset): 09:44:45.258949 bob.65514 > alice.8001: S 406012389:406012389(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2214891 0> 09:44:45.259415 alice.8001 > bob.65514: R 0:0(0) ack 406012390 win 0 09:44:51.217090 bob.65514 > alice.8001: S 406012389:406012389(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2214902 0> 09:44:51.217540 alice.8001 > bob.65514: R 0:0(0) ack 1 win 0 EXAMPLE WITH THE MODIFIED CODE Here we see the black network observed at alice-gw. One NTP exchange has been left in, since otherwise the red tcpdump would be empty. (The security policy does not require the observed NTP traffic to be in ESP.) 09:58:25.886014 bob.65513 > alice.8001: S 2189637913:2189637913(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2216532 0> 09:58:31.664971 bob.65513 > alice.8001: S 2189637913:2189637913(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2216543 0> 09:58:43.664091 bob.65513 > alice.8001: S 2189637913:2189637913(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2216567 0> 10:00:06.991381 alice.ntp > tai.ntp: v4 client strat 3 poll 6 prec -17 [tos 0x10] 10:00:06.991559 tai.ntp > alice.ntp: v4 server strat 3 poll 6 prec -18 [tos 0x10] 09:59:07.662368 bob.65513 > alice.8001: S 2189637913:2189637913(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2216615 0> Here we see the red network observed at alice-gw: 10:00:06.991356 alice.ntp > tai.ntp: v4 client strat 3 poll 6 prec -17 [tos 0x10] 10:00:06.991579 tai.ntp > alice.ntp: v4 server strat 3 poll 6 prec -18 [tos 0x10] With the modified code, we captured output of "netstat -p ipsec -s" on alice-gw immediately before and immediately after sending TCP SYNs. ipsec: 0 inbound packets processed successfully 0 inbound packets violated process security policy 0 inbound packets with no SA available 0 invalid inbound packets 0 inbound packets failed due to insufficient memory 0 inbound packets failed getting SPI 0 inbound packets failed on AH replay check 0 inbound packets failed on ESP replay check 0 inbound packets considered authentic 0 inbound packets failed on authentication 0 outbound packets processed successfully 0 outbound packets violated process security policy 0 outbound packets with no SA available 0 invalid outbound packets 0 outbound packets failed due to insufficient memory 0 outbound packets with no route ipsec: 0 inbound packets processed successfully 4 inbound packets violated process security policy 0 inbound packets with no SA available 0 invalid inbound packets 0 inbound packets failed due to insufficient memory 0 inbound packets failed getting SPI 0 inbound packets failed on AH replay check 0 inbound packets failed on ESP replay check 0 inbound packets considered authentic 0 inbound packets failed on authentication 0 outbound packets processed successfully 0 outbound packets violated process security policy 0 outbound packets with no SA available 0 invalid outbound packets 0 outbound packets failed due to insufficient memory 0 outbound packets with no route MODIFICATIONS For NetBSD netbsd-1-5: Index: src/sys/netinet/ip_input.c =================================================================== RCS file: /NETBSD-CVS/netbsd/src/sys/netinet/ip_input.c,v retrieving revision 1.1.1.1 diff -u -r1.1.1.1 ip_input.c --- src/sys/netinet/ip_input.c 2001/07/05 14:42:54 1.1.1.1 +++ src/sys/netinet/ip_input.c 2002/02/25 01:07:02 @@ -611,6 +611,15 @@ ipstat.ips_cantforward++; m_freem(m); } else { +#ifdef IPSEC + /* + * Enforce inbound IPsec SPD. + */ + if (ipsec4_in_reject(m, NULL)) { + ipsecstat.in_polvio++; + goto bad; + } +#endif /* * If ip_dst matched any of my address on !IFF_UP interface, * and there's no IFF_UP interface that matches ip_dst, For FreeBSD RELENG_4: Index: src/sys/netinet/ip_input.c =================================================================== RCS file: /FREEBSD-CVS/src/sys/netinet/ip_input.c,v retrieving revision 1.130.2.31 diff -u -r1.130.2.31 ip_input.c --- src/sys/netinet/ip_input.c 2001/12/15 01:06:27 1.130.2.31 +++ src/sys/netinet/ip_input.c 2002/02/24 16:10:26 @@ -625,8 +625,18 @@ if (ipforwarding == 0) { ipstat.ips_cantforward++; m_freem(m); - } else + } else { +#ifdef IPSEC + /* + * Enforce inbound IPsec SPD. + */ + if (ipsec4_in_reject(m, NULL)) { + ipsecstat.in_polvio++; + goto bad; + } +#endif /* IPSEC */ ip_forward(m, 0); + } #ifdef IPFIREWALL_FORWARD ip_fw_fwd_addr = NULL; #endif VENDOR STATUS This advisory was provided to KAME, NetBSD and FreeBSD before public posting. Our modifications above, or the equivalent, have already been incorporated into sys/netinet/ip_input.c in KAME's CVS repository (for NetBSD, 1.37 and for FreeBSD-4, 1.33), NetBSD -current (1.145) and 1.5-stable (1.114.4.8), and FreeBSD -current (1.192) and -stable (1.130.2.35).
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