---
id: CVE-2026-45905
title: 'xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path

  icmp_route_lookup() performs multiple route lookups to find a suitable
  route for sending ICMP error messages…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 <
    9a95ec9144eeff1fc6fbcc21b677e322c6f1430b
  - >-
    Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 <
    2c1f59005da9dd4b07b26984fd719e36557dc57c
  - >-
    Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 <
    b04061f89ffc6168e7ec3c71d0086ec3c3797228
  - >-
    Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 <
    1c9ef28f643cce34a6a6c36c8f4d6d60a60db7e1
  - >-
    Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 <
    423ce12d10b426709489d6b84fdaa6d2f31c5652
  - >-
    Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 <
    81b84de32bb27ae1ae2eb9acf0420e9d0d14bf00
  - Linux 2.6.25
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-06T15:44:09.393958Z'
published: '2026-05-27'
updated: '2026-11-06'
sourceUpdated: '2026-11-06T15:53:12.044Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-45905'
references:
  - url: 'https://git.kernel.org/stable/c/9a95ec9144eeff1fc6fbcc21b677e322c6f1430b'
  - url: 'https://git.kernel.org/stable/c/2c1f59005da9dd4b07b26984fd719e36557dc57c'
  - url: 'https://git.kernel.org/stable/c/b04061f89ffc6168e7ec3c71d0086ec3c3797228'
  - url: 'https://git.kernel.org/stable/c/1c9ef28f643cce34a6a6c36c8f4d6d60a60db7e1'
  - url: 'https://git.kernel.org/stable/c/423ce12d10b426709489d6b84fdaa6d2f31c5652'
  - url: 'https://git.kernel.org/stable/c/81b84de32bb27ae1ae2eb9acf0420e9d0d14bf00'
tags:
  - cve.org
epss: 0.00111
epssPercentile: 0.01357
ingestedAt: '2026-11-06T16:57:43.389Z'
---

## Overview

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

xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path

icmp_route_lookup() performs multiple route lookups to find a suitable
route for sending ICMP error messages, with special handling for XFRM
(IPsec) policies.

The lookup sequence is:
1. First, lookup output route for ICMP reply (dst = original src)
2. Pass through xfrm_lookup() for policy check
3. If blocked (-EPERM) or dst is not local, enter "reverse path"
4. In reverse path, call xfrm_decode_session_reverse() to get fl4_dec
   which reverses the original packet's flow (saddr<->daddr swapped)
5. If fl4_dec.saddr is local (we are the original destination), use
   __ip_route_output_key() for output route lookup
6. If fl4_dec.saddr is NOT local (we are a forwarding node), use
   ip_route_input() to simulate the reverse packet's input path
7. Finally, pass rt2 through xfrm_lookup() with XFRM_LOOKUP_ICMP flag

The bug occurs in step 6: ip_route_input() is called with fl4_dec.daddr
(original packet's source) as destination. If this address becomes local
between the initial check and ip_route_input() call (e.g., due to
concurrent "ip addr add"), ip_route_input() returns a LOCAL route with
dst.output set to ip_rt_bug.

This route is then used for ICMP output, causing dst_output() to call
ip_rt_bug(), triggering a WARN_ON:

 ------------[ cut here ]------------
 WARNING: net/ipv4/route.c:1275 at ip_rt_bug+0x21/0x30, CPU#1
 Call Trace:
  <TASK>
  ip_push_pending_frames+0x202/0x240
  icmp_push_reply+0x30d/0x430
  __icmp_send+0x1149/0x24f0
  ip_options_compile+0xa2/0xd0
  ip_rcv_finish_core+0x829/0x1950
  ip_rcv+0x2d7/0x420
  __netif_receive_skb_one_core+0x185/0x1f0
  netif_receive_skb+0x90/0x450
  tun_get_user+0x3413/0x3fb0
  tun_chr_write_iter+0xe4/0x220
  ...

Fix this by checking rt2->rt_type after ip_route_input(). If it's
RTN_LOCAL, the route cannot be used for output, so treat it as an error.

The reproducer requires kernel modification to widen the race window,
making it unsuitable as a selftest. It is available at:

  https://gist.github.com/mrpre/eae853b72ac6a750f5d45d64ddac1e81

## Affected

- `Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 < 9a95ec9144eeff1fc6fbcc21b677e322c6f1430b`
- `Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 < 2c1f59005da9dd4b07b26984fd719e36557dc57c`
- `Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 < b04061f89ffc6168e7ec3c71d0086ec3c3797228`
- `Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 < 1c9ef28f643cce34a6a6c36c8f4d6d60a60db7e1`
- `Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 < 423ce12d10b426709489d6b84fdaa6d2f31c5652`
- `Linux >= 8b7817f3a959ed99d7443afc12f78a7e1fcc2063 < 81b84de32bb27ae1ae2eb9acf0420e9d0d14bf00`
- `Linux 2.6.25`

## Remediation

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