In the Linux kernel, the following vulnerability has been resolved:
ipv4: icmp: reject RTN_UNREACHABLE input routes in icmp_route_lookup
When the forward output route cannot be used in icmp_route_lookup(),
it enters the "reverse path" and calls ip_route_input() on fl4_dec.daddr,
the original packet's source address.
ip_route_input() only returns an error for truly invalid packets. For
unreachable addresses it will succeed and return an input route whose
dst.output is set to ip_rt_bug(). The existing check only rejects
RTN_LOCAL routes, so the RTN_UNREACHABLE route types can still be returned
and later used for output, syzkaller triggering a WARN_ON_ONCE()
in ip_rt_bug() as bellow:
------------[ cut here ]------------
WARNING: net/ipv4/route.c:1273 at ip_rt_bug+0x14/0x20
RIP: 0010:ip_rt_bug+0x14/0x20
Call Trace:
ip_push_pending_frames+0xfa/0x100
__icmp_send+0x905/0xf10
ip_options_compile+0xc0/0xd0
ip_rcv_finish_core+0x321/0xae0
ip_rcv+0x1de/0x260
__netif_receive_skb_one_core+0x11a/0x130
netif_receive_skb+0x7b/0x260
tun_get_user+0x11bf/0x1c10
------------[ cut here ]------------
Reject input route that is RTN_UNREACHABLE to fix it. The net warning
is only printed for RTN_LOCAL, as RTN_UNREACHABLE is not the result of
a race condition.
ipv4: icmp: reject RTN_UNREACHABLE input routes in icmp_route_lookup
When the forward output route cannot be used in icmp_route_lookup(),
it enters the "reverse path" and calls ip_route_input() on fl4_dec.daddr,
the original packet's source address.
ip_route_input() only returns an error for truly invalid packets. For
unreachable addresses it will succeed and return an input route whose
dst.output is set to ip_rt_bug(). The existing check only rejects
RTN_LOCAL routes, so the RTN_UNREACHABLE route types can still be returned
and later used for output, syzkaller triggering a WARN_ON_ONCE()
in ip_rt_bug() as bellow:
------------[ cut here ]------------
WARNING: net/ipv4/route.c:1273 at ip_rt_bug+0x14/0x20
RIP: 0010:ip_rt_bug+0x14/0x20
Call Trace:
ip_push_pending_frames+0xfa/0x100
__icmp_send+0x905/0xf10
ip_options_compile+0xc0/0xd0
ip_rcv_finish_core+0x321/0xae0
ip_rcv+0x1de/0x260
__netif_receive_skb_one_core+0x11a/0x130
netif_receive_skb+0x7b/0x260
tun_get_user+0x11bf/0x1c10
------------[ cut here ]------------
Reject input route that is RTN_UNREACHABLE to fix it. The net warning
is only printed for RTN_LOCAL, as RTN_UNREACHABLE is not the result of
a race condition.
Metrics
Affected Vendors & Products
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Fixes
Solution
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Workaround
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References
History
Tue, 06 Oct 2026 14:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-20 CWE-704 |
Tue, 06 Oct 2026 09:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: ipv4: icmp: reject RTN_UNREACHABLE input routes in icmp_route_lookup When the forward output route cannot be used in icmp_route_lookup(), it enters the "reverse path" and calls ip_route_input() on fl4_dec.daddr, the original packet's source address. ip_route_input() only returns an error for truly invalid packets. For unreachable addresses it will succeed and return an input route whose dst.output is set to ip_rt_bug(). The existing check only rejects RTN_LOCAL routes, so the RTN_UNREACHABLE route types can still be returned and later used for output, syzkaller triggering a WARN_ON_ONCE() in ip_rt_bug() as bellow: ------------[ cut here ]------------ WARNING: net/ipv4/route.c:1273 at ip_rt_bug+0x14/0x20 RIP: 0010:ip_rt_bug+0x14/0x20 Call Trace: ip_push_pending_frames+0xfa/0x100 __icmp_send+0x905/0xf10 ip_options_compile+0xc0/0xd0 ip_rcv_finish_core+0x321/0xae0 ip_rcv+0x1de/0x260 __netif_receive_skb_one_core+0x11a/0x130 netif_receive_skb+0x7b/0x260 tun_get_user+0x11bf/0x1c10 ------------[ cut here ]------------ Reject input route that is RTN_UNREACHABLE to fix it. The net warning is only printed for RTN_LOCAL, as RTN_UNREACHABLE is not the result of a race condition. | |
| Title | ipv4: icmp: reject RTN_UNREACHABLE input routes in icmp_route_lookup | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-06T08:46:00.524Z
Reserved: 2026-09-25T10:25:14.338Z
Link: CVE-2026-98303
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-06T09:18:21.370
Modified: 2026-10-06T09:18:21.370
Link: CVE-2026-98303
Redhat
No data.
OpenCVE Enrichment
Updated: 2026-10-06T14:00:20Z