---
id: CVE-2026-53267
title: 'netfilter: nft_ct: bail out on template ct in get eval'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  netfilter: nft_ct: bail out on template ct in get eval

  I noticed this issue while looking at a historic syzbot report [1].

  A rule like the one below is enough to trig…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 <
    af80f78ce984649e1698b841cd33f4fa505ad828
  - >-
    Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 <
    8470f676eadeab99132708acb1a85915664d6115
  - >-
    Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 <
    f071b0bf078146368d18e4eec386bf2ddc0ab7e0
  - >-
    Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 <
    2e154b5f53f1b0b490c7b8b02499f90feb86b1d5
  - >-
    Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 <
    3027ecbdb5fdf9200251c21d4818e4c447ef78e1
  - Linux 4.1
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:28:07.142807Z'
published: '2026-06-25'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:31:44.472Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-53267'
references:
  - url: 'https://git.kernel.org/stable/c/af80f78ce984649e1698b841cd33f4fa505ad828'
  - url: 'https://git.kernel.org/stable/c/8470f676eadeab99132708acb1a85915664d6115'
  - url: 'https://git.kernel.org/stable/c/f071b0bf078146368d18e4eec386bf2ddc0ab7e0'
  - url: 'https://git.kernel.org/stable/c/2e154b5f53f1b0b490c7b8b02499f90feb86b1d5'
  - url: 'https://git.kernel.org/stable/c/3027ecbdb5fdf9200251c21d4818e4c447ef78e1'
tags:
  - cve.org
epss: 0.0012
epssPercentile: 0.01678
ingestedAt: '2026-10-16T17:24:46.740Z'
---

## Overview

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

netfilter: nft_ct: bail out on template ct in get eval

I noticed this issue while looking at a historic syzbot report [1].

A rule like the one below is enough to trigger the bug:

    table ip t {
        chain pre {
            type filter hook prerouting priority raw;
            ct zone set 1
            ct original saddr 1.2.3.4 accept
        }
    }

The first expression attaches a per-cpu template ct via
nft_ct_set_zone_eval() (nf_ct_tmpl_alloc -> kzalloc, tuple is all
zero, nf_ct_l3num(ct) == 0). The next expression then calls
nft_ct_get_eval() on the same skb, treats the template as a real ct
and hits the 16-byte memcpy path. With dreg at NFT_REG32_15 this
overflows past struct nft_regs on the kernel stack; with smaller
dreg values it silently clobbers adjacent registers.

Reject template ct at the eval entry and in nft_ct_get_fast_eval(),
mirroring the check nft_ct_set_eval() already has. Additionally,
bound the address copy in NFT_CT_SRC / NFT_CT_DST by priv->len
instead of by nf_ct_l3num(ct): nf_ct_get_tuple() zeroes the tuple
before pkt_to_tuple() fills in only the protocol-relevant leading
bytes, so the trailing bytes of tuple->{src,dst}.u3.all are
well-defined zero. priv->len is validated at rule load, so the
copy size is now bounded by the destination register rather than
by an untrusted field on the conntrack.

[1]: https://syzkaller.appspot.com/bug?id=389cf09cb72926114fce90dc85a2c3231dcb647c

## Affected

- `Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 < af80f78ce984649e1698b841cd33f4fa505ad828`
- `Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 < 8470f676eadeab99132708acb1a85915664d6115`
- `Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 < f071b0bf078146368d18e4eec386bf2ddc0ab7e0`
- `Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 < 2e154b5f53f1b0b490c7b8b02499f90feb86b1d5`
- `Linux >= 45d9bcda21f4c13be75e3571b0f0ef39e77934b5 < 3027ecbdb5fdf9200251c21d4818e4c447ef78e1`
- `Linux 4.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.