---
id: "CVE-2026-98485"
kind: "vulnerability"
aliases: ["CVE-2026-98485"]
title: "Linux kernel: crafted IPv6 packet triggers out-of-bounds read in netfilter"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "ipv6", "linux", "netfilter", "self-hosted"]
not_affected_if: ["no-ip6t-rt-rules", "no-ipv6"]
published_at: "2026-10-18T16:16:59+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:25:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98485", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel: crafted IPv6 packet triggers out-of-bounds read in netfilter

The netfilter ip6t_rt match module lets a rule with zero addresses and non-strict address matching loop past its array bounds. A crafted IPv6 packet with matching routing addresses makes the kernel read beyond the rule structure, causing kernel warnings or a crash.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the running kernel version with `uname -r` and compare it to the fixed kernel release in the linked kernel commits.
- Look for netfilter rules using the `rt` match with `--rt-type` or `--rt-segsleft` address matching in `ip6tables-save` output, for example `ip6tables-save | grep 'rt'`.

## Fix

- Update the Linux kernel to a release that includes the upstream fix for ip6t_rt (the fix rejects rules with address matching and zero addresses, and fixes the loop termination).
- Until patched, remove any ip6tables rules that use the rt match with address matching options.

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98485

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ip6t_rt: fix zero-address non-strict match out-of-bounds read

rt_mt6_check() permits rules to be configured with rtinfo->addrnr == 0
even when address matching (IP6T_RT_FST_MASK) is requested.

In the IP6T_RT_FST_NSTRICT path, rt_mt6() evaluates packet routing
addresses against rtinfo->addrs[i] and terminates backwards at the bottom
of the loop:

    if (ipv6_addr_equal(ap, &rtinfo->addrs[i])) {
        i++;
    }
    if (i == rtinfo->addrnr)
        break;

When addrnr is 0, if the first packet address matches rtinfo->addrs[0],
i is incremented to 1. Because i is now strictly greater than addrnr (0),
the loop termination condition (i == rtinfo->addrnr) is bypassed and will
never be satisfied.

If a crafted IPv6 packet contains matching routing addresses, i will
advance past IP6T_RT_HOPS (16). The subsequent call to ipv6_addr_equal()
reads beyond struct ip6t_rt, triggering UBSAN/KASAN out-of-bounds warnings
or kernel panics.

Fix this by:
1. Rejecting rules in rt_mt6_check() where IP6T_RT_FST_MASK is set but
   rtinfo->addrnr is zero.
2. In rt_mt6(), moving the termination condition (i < rtinfo->addrnr)
   into the for-loop header condition and removing the backwards break
   at the end of the loop body.

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