# CVE-2026-98303: ipv4: icmp: reject RTN_UNREACHABLE input routes in icmp_route_lookup

> A flaw in the Linux kernel's ICMP handling allows remote attackers to trigger a kernel warning and potential denial of service by sending crafted packets.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106167, BELL-CVE-2026-98303, DEBIAN-CVE-2026-98303, GHSA-hw8j-26f4-2863, UBUNTU-CVE-2026-98303

## What is CVE-2026-98303?

CVE-2026-98303 is a denial of service vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

## Which versions are affected by CVE-2026-98303?


## How do I fix CVE-2026-98303?

Apply the vendor's patch.

## Is CVE-2026-98303 being exploited?

There is no known exploitation of CVE-2026-98303 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98303 and fix it if it is affected.

What it is: CVE-2026-98303 is a denial of service vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98303 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98303/ (Markdown: https://insights.sbomify.com/CVE-2026-98303/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98303
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98303
- OSV: https://osv.dev/vulnerability/CVE-2026-98303

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98303/
Summaries are generated and may contain mistakes; the official description above is the record.