UBUNTU-CVE-2026-45905
In the Linux kernel, the following vulnerability has been resolved: xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path icmp_route_lookup() performs multiple route lookups to find a suitable route for sending ICMP error messages, with special handling for XFRM (IPsec) policies. The lookup sequence is: 1. First, lookup output route for ICMP reply (dst = original src) 2. Pass through xfrm_lookup() for policy check 3. If blocked (-EPERM) or dst is not local, enter "reverse path" 4. In reverse path, call xfrm_decode_session_reverse() to get fl4_dec which reverses the original packet's flow (saddr<->daddr swapped) 5. If fl4_dec.saddr is local (we are the original destination), use __ip_route_output_key() for output route lookup 6. If fl4_dec.saddr is NOT local (we are a forwarding node), use ip_route_input() to simulate the reverse packet's input path 7. Finally, pass rt2 through xfrm_lookup() with XFRM_LOOKUP_ICMP flag The bug occurs in step 6: ip_route_input() is called with fl4_dec.daddr (original packet's source) as destination. If this address becomes local between the initial check and ip_route_input() call (e.g., due to concurrent "ip addr add"), ip_route_input() returns a LOCAL route with dst.output set to ip_rt_bug. This route is then used for ICMP output, causing dst_output() to call ip_rt_bug(), triggering a WARN_ON: ------------[ cut here ]------------ WARNING: net/ipv4/route.c:1275 at ip_rt_bug+0x21/0x30, CPU#1 Call Trace: <TASK> ip_push_pending_frames+0x202/0x240 icmp_push_reply+0x30d/0x430 __icmp_send+0x1149/0x24f0 ip_options_compile+0xa2/0xd0 ip_rcv_finish_core+0x829/0x1950 ip_rcv+0x2d7/0x420 __netif_receive_skb_one_core+0x185/0x1f0 netif_receive_skb+0x90/0x450 tun_get_user+0x3413/0x3fb0 tun_chr_write_iter+0xe4/0x220 ... Fix this by checking rt2->rt_type after ip_route_input(). If it's RTN_LOCAL, the route cannot be used for output, so treat it as an error. The reproducer requires kernel modification to widen the race window, making it unsuitable as a selftest. It is available at: https://gist.github.com/mrpre/eae853b72ac6a750f5d45d64ddac1e81
02 / AFFECTED SOFTWARE
Affected packages
7 explicit affected versions
10 explicit affected versions
11 explicit affected versions
120 explicit affected versions
6 explicit affected versions
53 explicit affected versions
116 explicit affected versions
89 explicit affected versions
50 explicit affected versions
6 explicit affected versions
12 explicit affected versions
24 explicit affected versions
19 explicit affected versions
10 explicit affected versions
6 explicit affected versions
100 explicit affected versions
61 explicit affected versions
85 explicit affected versions
84 explicit affected versions
91 explicit affected versions
86 explicit affected versions
76 explicit affected versions
10 explicit affected versions
36 explicit affected versions
26 explicit affected versions
90 explicit affected versions
191 explicit affected versions
7 explicit affected versions
84 explicit affected versions
39 explicit affected versions
13 explicit affected versions
85 explicit affected versions
43 explicit affected versions
35 explicit affected versions
51 explicit affected versions
50 explicit affected versions
18 explicit affected versions
42 explicit affected versions
118 explicit affected versions
64 explicit affected versions
44 explicit affected versions
11 explicit affected versions
13 explicit affected versions
4 explicit affected versions
121 explicit affected versions
23 explicit affected versions
51 explicit affected versions
124 explicit affected versions
1 explicit affected versions
1 explicit affected versions
21 explicit affected versions
7 explicit affected versions
16 explicit affected versions
10 explicit affected versions
20 explicit affected versions
76 explicit affected versions
33 explicit affected versions
47 explicit affected versions
8 explicit affected versions
7 explicit affected versions
12 explicit affected versions
11 explicit affected versions
111 explicit affected versions
7 explicit affected versions
12 explicit affected versions
14 explicit affected versions
10 explicit affected versions
10 explicit affected versions
1 explicit affected versions
7 explicit affected versions
16 explicit affected versions
104 explicit affected versions
12 explicit affected versions
105 explicit affected versions
12 explicit affected versions
40 explicit affected versions
120 explicit affected versions
45 explicit affected versions
16 explicit affected versions
17 explicit affected versions
27 explicit affected versions
10 explicit affected versions
37 explicit affected versions
10 explicit affected versions
11 explicit affected versions
13 explicit affected versions
38 explicit affected versions
3 explicit affected versions
10 explicit affected versions
11 explicit affected versions
68 explicit affected versions
1 explicit affected versions
26 explicit affected versions
9 explicit affected versions
13 explicit affected versions
144 explicit affected versions
37 explicit affected versions
1 explicit affected versions
29 explicit affected versions
111 explicit affected versions
13 explicit affected versions
12 explicit affected versions
96 explicit affected versions
40 explicit affected versions
39 explicit affected versions
8 explicit affected versions
1 explicit affected versions
100 explicit affected versions
92 explicit affected versions
55 explicit affected versions
33 explicit affected versions
23 explicit affected versions
60 explicit affected versions
10 explicit affected versions
19 explicit affected versions
188 explicit affected versions
18 explicit affected versions
11 explicit affected versions
5 explicit affected versions
12 explicit affected versions
11 explicit affected versions
7 explicit affected versions
12 explicit affected versions
10 explicit affected versions
16 explicit affected versions
138 explicit affected versions
2 explicit affected versions
5 explicit affected versions
77 explicit affected versions
132 explicit affected versions
39 explicit affected versions
93 explicit affected versions
165 explicit affected versions
154 explicit affected versions
10 explicit affected versions
26 explicit affected versions
7 explicit affected versions
1 explicit affected versions
69 explicit affected versions
35 explicit affected versions
46 explicit affected versions
11 explicit affected versions
13 explicit affected versions
45 explicit affected versions
139 explicit affected versions
78 explicit affected versions
16 explicit affected versions
91 explicit affected versions
49 explicit affected versions
116 explicit affected versions
3 explicit affected versions
132 explicit affected versions
93 explicit affected versions
1 explicit affected versions
7 explicit affected versions
2 explicit affected versions
15 explicit affected versions
51 explicit affected versions
98 explicit affected versions
16 explicit affected versions
92 explicit affected versions
18 explicit affected versions
41 explicit affected versions
12 explicit affected versions
71 explicit affected versions
80 explicit affected versions
7 explicit affected versions
1 explicit affected versions
27 explicit affected versions
66 explicit affected versions
121 explicit affected versions
1 explicit affected versions
1 explicit affected versions
10 explicit affected versions
42 explicit affected versions
8 explicit affected versions
55 explicit affected versions
5 explicit affected versions
8 explicit affected versions
45 explicit affected versions
13 explicit affected versions
110 explicit affected versions
13 explicit affected versions
72 explicit affected versions
7 explicit affected versions
140 explicit affected versions
8 explicit affected versions
94 explicit affected versions
10 explicit affected versions
12 explicit affected versions
9 explicit affected versions
39 explicit affected versions
108 explicit affected versions
80 explicit affected versions
56 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
49 explicit affected versions
14 explicit affected versions
38 explicit affected versions
167 explicit affected versions
9 explicit affected versions
17 explicit affected versions
38 explicit affected versions
17 explicit affected versions
14 explicit affected versions
92 explicit affected versions
6 explicit affected versions
97 explicit affected versions
121 explicit affected versions
4 explicit affected versions
81 explicit affected versions
10 explicit affected versions
1 explicit affected versions
1 explicit affected versions
1 explicit affected versions
91 explicit affected versions
80 explicit affected versions
79 explicit affected versions
13 explicit affected versions
43 explicit affected versions
77 explicit affected versions
16 explicit affected versions
119 explicit affected versions
10 explicit affected versions
8 explicit affected versions
44 explicit affected versions
88 explicit affected versions
14 explicit affected versions
4 explicit affected versions
78 explicit affected versions
14 explicit affected versions
11 explicit affected versions
1 explicit affected versions
69 explicit affected versions
123 explicit affected versions
18 explicit affected versions
38 explicit affected versions
80 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path icmp_route_lookup() performs multiple route lookups to find a suitable route for sending ICMP error messages, with special handling for XFRM (IPsec) policies. The lookup sequence is: 1. First, lookup output route for ICMP reply (dst = original src) 2. Pass through xfrm_lookup() for policy check 3. If blocked (-EPERM) or dst is not local, enter "reverse path" 4. In reverse path, call xfrm_decode_session_reverse() to get fl4_dec which reverses the original packet's flow (saddr<->daddr swapped) 5. If fl4_dec.saddr is local (we are the original destination), use __ip_route_output_key() for output route lookup 6. If fl4_dec.saddr is NOT local (we are a forwarding node), use ip_route_input() to simulate the reverse packet's input path 7. Finally, pass rt2 through xfrm_lookup() with XFRM_LOOKUP_ICMP flag The bug occurs in step 6: ip_route_input() is called with fl4_dec.daddr (original packet's source) as destination. If this address becomes local between the initial check and ip_route_input() call (e.g., due to concurrent "ip addr add"), ip_route_input() returns a LOCAL route with dst.output set to ip_rt_bug. This route is then used for ICMP output, causing dst_output() to call ip_rt_bug(), triggering a WARN_ON: ------------[ cut here ]------------ WARNING: net/ipv4/route.c:1275 at ip_rt_bug+0x21/0x30, CPU#1 Call Trace: <TASK> ip_push_pending_frames+0x202/0x240 icmp_push_reply+0x30d/0x430 __icmp_send+0x1149/0x24f0 ip_options_compile+0xa2/0xd0 ip_rcv_finish_core+0x829/0x1950 ip_rcv+0x2d7/0x420 __netif_receive_skb_one_core+0x185/0x1f0 netif_receive_skb+0x90/0x450 tun_get_user+0x3413/0x3fb0 tun_chr_write_iter+0xe4/0x220 ... Fix this by checking rt2->rt_type after ip_route_input(). If it's RTN_LOCAL, the route cannot be used for output, so treat it as an error. The reproducer requires kernel modification to widen the race window, making it unsuitable as a selftest. It is available at: https://gist.github.com/mrpre/eae853b72ac6a750f5d45d64ddac1e81
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/81b84de32bb27ae1ae2eb9acf0420e9d0d14bf00
- https://ubuntu.com/security/CVE-2026-45905
- https://ubuntu.com/security/notices/USN-8492-1
- https://ubuntu.com/security/notices/USN-8492-2
- https://ubuntu.com/security/notices/USN-8492-3
- https://ubuntu.com/security/notices/USN-8492-4
- https://ubuntu.com/security/notices/USN-8492-5
- https://ubuntu.com/security/notices/USN-8497-1
- https://ubuntu.com/security/notices/USN-8498-1
- https://ubuntu.com/security/notices/USN-8499-1
- https://ubuntu.com/security/notices/USN-8606-1
- https://ubuntu.com/security/notices/USN-8607-1
- https://ubuntu.com/security/notices/USN-8609-1
- https://ubuntu.com/security/notices/USN-8619-1
- https://www.cve.org/CVERecord?id=CVE-2026-45905