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Fencer Vulns
medium 4.7

CVE-2026-45905 json

xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path

published 2026-05-27 5 mo ago modified 2026-11-06 2 d ago also EUVD-2026-32371

cvss
4.7
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 1%
public exploits
0
none known

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, 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

Patch / fix

  • Linux Linux 6.1.165, 6.6.128, 6.12.75, 6.18.14, 6.19.4, 7.0
  • linux Debian 12 6.1.170-1
  • linux Debian 13 6.12.85-1
  • linux Debian 14 6.18.14-1

debian advisories DEBIAN-CVE-2026-45905

  • linux Ubuntu 24.04 LTS 6.8.0-134.134
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1060.63
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1063.69
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1058.64
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1060.61
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1063.71
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1045.48
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1060.64

ubuntu advisories UBUNTU-CVE-2026-45905

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.72.1
  • kernel-syms-rt Real Time Module 15 SP7 6.4.0-150700.7.72.1
  • kernel-source-rt Real Time Module 15 SP7 6.4.0-150700.7.72.1
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.78.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.78.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.78.1
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.78.1
  • kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.78.1

suse advisories SUSE-SU-2026:3810-1SUSE-SU-2026:3790-1SUSE-SU-2026:23244-1SUSE-SU-2026:23241-1SUSE-SU-2026:23194-1SUSE-SU-2026:23193-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.37.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.37.1

opensuse advisories openSUSE-SU-2026:21555-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-45905 updated cvss 5.5

kernel: xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: no fix available, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 kernel
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 d ago

Exploit prediction

0.11% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.